When the Wise Man Points at the Moon the Fool Looks at the Wise Man's Finger

  [Sorry for the light writing, but October is a busy month around my house with 3 birthdays in 2 weeks.]
  Over the weekend I was talking with my sons about gaming (ok, ok - that can describe every day) when the oldest, J., and I had this exchange:
  J: "Didn't some of the high-level wizards in Greyhawk keep clones on their moon?"
  Me: "Yup"
  J: "How'd they get there?"
  Me: "How do you think?"
  J: "Well, maybe the air doesn't end between the surface and the moon, there. Or maybe they had something like an Apparatus of Kwalish that could fly."
  Me: "Think easier."
  J: .... "Hey! Teleport! Holy Moley - they can see the destination! It isn't even tough! And if they have Teleport without Error it's a cakewalk! Wow! The implications are HUGE!"

  Yes. Yes, they are.
  Let's talk about Teleport and the implications, shall we?
  First, the AD&D 1e (and OSRIC) description of Teleport is pretty fun: It can't cross dimensional boundaries, but distance isn't a factor. That's pretty cool. Add in that the description says 'instantly' so there is no lag. It can be dangerous, though - if you aren't very familiar with where you are going you might end up rather dead. It is certainly meant mainly as a 'get out of jail free' card - in a tight spot you and your pals can get home. And if you are willing to accept some risk you could ambush the jeebers out of someone.

  But can you go to the moon?
  Well, on a clear night you can see the moon, right? Sure, it is far away, but distance means nothing to the spell. I might argue that your inability to see precise details at the incredible range means you'd max out at 'seen casually' until you actually got there, but that risk isn't that bad, and you could mitigate it a little. And once you got there you could certainly find some place, spend a few days there, and have a 'carefully studied' target location for future trips.
  So, yeah - it looks like any 9th+ level wizard with access to the Teleport spell has Faster Than Light space travel, at least to the moon. And if, like me, you have Teleport without Error in your campaign that means that 14th+ level wizards can do so with essentially no risk!

  "But Rick," you say, "The moon is an arid, airless rock! Who could live there?"
  Well, your moon(s) could be different. A little air, maybe a bit of water like a desert? Or perhaps it is another world; unique plants, animals, even its own humanoids and civilizations.
  Sounds like a lot of work, huh?
  But even if it is an arid, airless rock - that's awesome! Between Necklaces of Adaptation, Helms of Underwater Action, and spells a powerful mage is going to see vacuum as a feature, not a bug. After all, it makes his remote wizard's tower even harder to attack, right?
  Imagine it!  An archmage's tower jutting up from the rim of a lunar crater, the crater itself 'roofed over' with Walls of Force and filled with a massive garden and small forest. Other Walls of Force keeping air within the tower. Occasionally servants of the archmage venture out in an Apparatus of Kwalish to retrieve unique gemstones for their master's research.
  Then ages pass. The overgrown garden is withered and desiccated in the vacuum decades after the Walls of Force failed. The now-airless tower still looms over the lifeless moonscape as the archmage lich, unconcerned with breathing, watches over his sterile kingdom....

  That could be a ton of fun.
  Or perhaps the moon is a secret dock for spelljammers and powerful mages control the (rather exotic) trade with other spheres and treat any newcomer as competition or a smuggler?
  Or the moon is the headquarters for an illithid invasion. Or it is the forgotten birthplace of the elves and is still populated by a strange elven race with access to unique magic. Or there is air between the planet and the moon and the moon is the breeding ground and nesting place for the most powerful dragons - the only creatures powerful enough to fly that vast distance. The catch is only the youngest, weakest dragons remain on the planet, meaning that the youngest, weakest moon dragons are larger, smarter, and tougher than any great elder wyrm ever seen....

  No, I'm not done.
  Think of the planets!

  "Whoa, whoa, WHOA!" you say, "Rick, I might let a powerful mage Teleport to the moon with great risk, but planets?! They're just points of light in the sky! I wouldn't even allow a PC to Teleport as 'casually seen!"

  Yeah. I wouldn't either. Or I might let you and have you end up in deep space or the center of the planet.

  But!

  Let's say your mage has been to the moon. She thinks it is nice, but too crowded. Planets are interesting because they act unusually - what if they're like the moon, but further away? Your 15th level mage knows how hideously risky it would be to Teleport towards something so obscure, but she has an idea.

  Ever read the description of the spell Clairvoyance? I mean, really looked at it, especially since you read about jaunting to the moon? Guess what? In 1e, OSRIC, etc. it's like Teleport:
  No range, it just can't cross the planes.
  So if a curious and ambitious mage of sufficient power were to want to they could, over the course of weeks, easily cast Clairvoyance multiple times on a planet until they 'zoomed in' on the surface and could get a clear look at it. They could scan for a safe place to 'land', learn about any local plant or animal life, etc. long before they actually went there.
  Oh, and Crystal Balls work the same way, even with time limits.

  And I don't know about you, but if a 9th level magic-user had Clairvoyance active and attempted to Teleport to the scryed location, I would probably rule that to be 'studied carefully' and no risk at all for Teleport without Error.

  If I may engage in a little emotional display.
  ahem
  Sweet Baby John the Baptist! Do you know what this means?! This means every wizard that knows both Clairvoyance and Teleport is effectively a one-man space program with access to FTL travel!
  If you have Teleport without Error or similar in your campaign it means there isn't even that much risk involved!

  Let that sink in for a moment. Savor the possibilities. Here's a few off the top of my head:
  - Multi-genre adventures in any campaign.
  - Every intelligent race came from other planets
  - Evil space-thieves smuggling blaster rifles to the Hobgoblin King
  - Encounters with a group of people in strange clothes that ask to be 'beamed up' and then vanish in front of the players
  - The ability to hire mercenaries from another planet
  - Remaking Episode I in my 1e campaign with monks FROM SPACE, bards FROM SPACE, and a horde of zombies for the bad guys

  I mean, talking about what could be done with this would be a year of blog posts.

  So - what are YOU going to do with space-mages?