A few days back I read an commented on this post http://eiglophian.blogspot.com/2010/04/spell-point-systems.html regarding spell point systems. I freely admit to using them myself in games past, one of my longest running AD&D campaigns actually used a spell point system.
Here is my recollection of it(can't find the whole system in old notes).
spell memorization- you still had to memorize the spells you wanted to use ahead of time. I now we fiddled with many versions but may have rested on a total number of spells equal to caster level plus number of known languages in spells that could be prepared at one time. One still couldn't access a spell of a given level until their class would normally permit.
I called spell points Manna. Every class had some Manna points. One had to have a Manna score of 1 or more to use magic items. Potions,Magic armor and weapons simply didn't work for folks with 0 Manna. Some magical items used up manna points per use.
Manna Dice by class: MU/Illusionist- 1d10, Druid/Cleric- 1d8, Ranger/Paladin- 1d6, everyone else 1d4. Spell casting classes got a bonus equivalent to Con for hp when calculating MP. As this was AD&D at the time single class MU's got the higher bonuses as fighters did with HP.
Spell Casting- 1d8 MP were used per spell level when a spell was cast in moderately favorable conditions. Improved conditions reduced the size of the dice, bad ones increased the size og the dice. If one ended up with a spell trying to use more Manna then the spell caster has they took the difference in damage, the spell failed and there was a chance of a more serious magical mishap with a chance equal to extra MP x Spell level trying to be cast.
There were a few extra spells that dealt with the Manna Points, spells that would lend, steal or blast away MP, spells that would tap into, trap and seal Ley lines and magical fonts. We had magical storage devices the ever popular potion of rejuvenation that restored hp and mp.
This system ultimately resulted in high level MUs that used darn few high level spells, Fly, Fireball, Haste and Lightning Bolt were very popular. Some of the more esoteric low level spells did see a little more use (Grease was oddly popular) but in general folks geared in on the 3rd and 4th level boom-zap spells and magic system manipulating spells.
The camapign that used this system lasted for about 8 years(with the magic system being more or less intact the last 3) so in a way it was a success but it also required a lot more book keeping.