I used to award by-the-book exp, CR & EL against total number of people in the party and their levels, and the calculations were just ridiculous. I hated having to pull out a computer just to do the experience point calculations.
I also thought the curve was set very high for progress. I run somewhat challenging games, and after only one or two sessions the by-the-book XP said PC's should be levelling. A dungeon crawl adventure I ran that I (and my players) thought was challenging and fun was almost two levels worth of XP for just two sessions of adventuring.
I hated for things to level up that fast, and so did my players. Getting nifty new powers is cool, but you are barely learning to use your older ones if you're levelling after almost every new adventure. Since higher level D&D is, frankly, much harder to run (when PC's have abilities that can sidestep entire encounters and puzzles with one spell), savoring the time at the lower levels before the game becomes more of a headache to run is also a DM's pleasure.
Then I said Forget It. I moved to strictly story-based experience. In a typical game, a character recieves 250 x Current Character Level. A character will level every 4 sessions. If they spend XP for spells or magic items, then slower, for excellent roleplaying/creative thinking/other commendable acts I'll award an extra 50 x character level XP.
The game progresses a little slower, but my players have enjoyed it. The game isn't about PC's trying to get into as many fights as possible to rack up as much experience as possible, or trying to take on big things because they'll know they can get the big XP, it has made it more about roleplaying and less about the metagame aspect of getting as much XP as possible.
As for when I actually award it? I try to at the end of a session, but the complexities of the CR/APL system were so complicated that I'd have to spend significant time after the module calculating experience, then give it out at the beginning of the next session (or email/call players and tell them).
I'm sure some of you will think it's not that complicated, but how quickly could you do experience for an encounter like:
3 7th Level PC, 2 6th Level PC's & 3 5th Level PC's vs. 4 Ogre Barbarian 1's, 20 Orc Warrior 1's, 4 Orc Fighter 1's, 1 Orc Fighter 6/Blackguard 1, 2 Half-Orc Monk 4's, and 1 Human Cleric 9 (a typical climactic encounter of an adventure). In other words, the PC's against a cult leader, his bodyguard, a pair of monastic acolytes, and a small detachment of guards.