It is to a degree...it doesn't "add" detail and it won't magically turn into a HD disc, but if the scaling chip inside (Faroudja =awesome) is good, it will make a good looking DVD a littel better. Keep in mind, that the results aren't eye popping or such, as it's still just a DVD but try a good upscaling player at 720p or 1080i for a few weeks, and then go back to 480p or 480i, and you'll notice the image being much much softer.
If there is one bad thing about it, it is that on certain displays ( plasmas being a prime offender, upscaling with a Faroudja chip will introduce some macroblocking in certain scenes of certain DVD's. A famous disc is Star Wars AOTC, with the scene in Palpatine's office with Yoda nad Sam Jackson...at one part, the walls look alive!!
Keep in mind, that it is display dependant though...some don't have the problem at all, and on my LCD proj, I don't see the fuss.