I managed to trim 13 roms and still have around 64 megs to squeeze in a 512 cart. Here is my list
Advance Wars
Bomberman
Castlevania -DOS
Mario and Luigi - PIT
Mario Kart DS
MegaMan ZX
Meteos
NSMB
Phoenix Wright
Tetris DS
Trauma Center
Viewtiful Joe
WarioWare.
That's more than I could ever play all at once. 512 is enough for some, but maybe not all. If you don't like it, just don't get it and wait for the acekard.
Have you tried using single-cart multiplayer with trimmed roms? The gbatemp review used non-trimmed roms, just wondering if it works the same in both situations.