It does work, and it's what I did for a long time. But a standalone DVD player is much less hassle, responds more quickly, has a remote control, and is much less sensitive to scratches and dirt on discs. (Computer DVD-ROM drives are designed to be super-picky about data integrity.) Also, a standalone DVD player will pass on closed-captioning info to the TV; the computer can render them itself, but the TV's text will be crisper.
So yeah, for $20-50, it's just not worth using the computer.
tooki