I play Age of Empires on the DS, but am seriously careful. When playing a match against 2 to 3 opponents, the maximum in the game, it's very odd. Having to many units out on the board the game lags, and eventually freezes during the battle animations. I sometimes try to save preemptively, but it will sometimes say "Could not write data, turn off power and remove game card". Then again, it's got PS1&1/2 graphics, so maybe the ram on the ds couldn't take it.
Well if I'm still speaking of ram on handheld systems then Mana Khemia sometimes lags before battles, though only visually. Then it works for the rest of the time. Though it did freeze on the grow book once...just once.
Then the most epic bug/lag that's ever happened to me:
I decided to make a new character back when I still played WoW. It was a mage, and as you WoW players are aware the first spell they know is the basic fireball. So I found a wolf as part of the beginners quests in the human starting area. I clicked on the fireball spell, as it was charging it didn't necessarily lag, it just...froze on me. It returned to normal about a few seconds later and the only thing I saw was that I was no longer charging the fireball, and that an explosion appeared on the wolf, instantly killing it. It was fucking awesome.