I do in most games... In Killzone 2 I do because its sometimes infuriating to have to reload during a shootout. If the enemie's close though, I would usually switch to my pistol if my clip runs dry. But if It's a long range shootout, Id get to some cover to reload. To avoid this though, I reload as soon as possible.
It was also nice that the game rewarded me with a Trophy for 150 manual reloads... I was quite happy with that.
In the game Black however, Reloading is usually a no-no. As you see, the creators of black were the only developers that I know of who were smart enough to release that by taking out a clip with ammo in it, you lose that ammo from your total amount... Which makes sense right?
But ammo was pretty common if I remember correctly. And after completing it once, you unlock silver weopons, which means unlimited ammo. So reloading was no longer a problem.
In the 5 pages of replies I hope I wasn't the only one to mention those two games, because those are the 2 best serious FPS I've ever played.
EDIT:Excellent... Somebody else mentioned Black and its excellent reloading system, and they explained it much better than I did.
Dead Raen said:
The game BLACK had a unique system where the rounds from your magazine weren't pooled into the rest of your ammo reservoir, and reloading after a single kill could cost an entire magazine.
Ever since BLACK, I've waited until about 1/5th of my magazine remains before reloading, or until the action has died down.