I've had 2 experiences with an adapter. 1: Using with an IDE to USB enclosure to recover some data of a drive, which it did not work at all. 2: One using a 500gb SATA hdd in my xbox, which has been working wonderfully for a while now. One of the best things I can think of is rolling over to newegg and checking out some of the reviews there.
EDIT: I haven't noticed any slowness from the adapter. The videos play just as smooth and games load just as quickly as they did with my ide 250gb drive I had in there previously.