The Blackstone campaign is currently the 'main game' I am running. I has been ongoing for 3 years and is still strong. I use 2nd Edition AD&D with all the Player's Option books but not all of the options allowed.
The main differences for casters are I allow customized magic-users and clerics and that I use the spell point system as detailed in Spells and Magic for all casters and conditional modifiers for Clerics.
I originally added this to the campaign for three reasons - I like the flexibility the spell point system gives casters; the conditional modifiers add some depth to religion; and I have a major campaign artifact based on the system that s a huge plot driver.
Unfortunately, I now wish I hadn't used the spell point system! The party consists of a Human Thief, a Human Magic-user (Generalist), a Human Magic-User (Fire Elementalist), a Human Fighter, and a Half-Elven Cleric/Magic-user. That's right, 3 of the 5 are spell casters. This means that the group sits down about 40 minutes before play is scheduled and spends all of that time selecting spells. Even with lists of default spells the desire to customize your spell list is too great and the point system really encourages min/maxing to squeeze out very possible spell. Toss in high stats (bonus points), specialization (points that can only be used for particular types of spells), and the cleric of a God of Magic (casting his clerical spells sometimes costs more points, other times it costs less, resulting in 'left over' points that can be used for all sorts of mischief) and it is a major headache before and during each session.
For more goodness, this means I have to do the same for all spell casting NPCs!
Now, I have no issue with point systems per se; Rolemaster is probably my favorite magic system and it is all about points, discounts, and arcane rules. No, my problem is that it drastically changes D&D - character creation, development, and play are all very different. A spell casting character with a good knowledge of the point system 'punches above his weight' and should be counted 1 to 5 levels higher (depending on overall level) for purposes of adventure planning. And, in the end, it isn't vancian enough to match the rest of AD&D. Magic items end up not working properly (Rings of Wizardry are the obvious issue, but what about a Pearl of Power? Incense of Meditation?).
I will not use the spell point system in AD&D again, but I will keep it in the Blackstone campaign. Why? It is part of the woof and weave of that world, now, and besides - I still have that plot-driving artifact lurking about.