The players simply take the native 480 lines of the DVD and then interpolates the data to increase the number of lines to an HDTV's native resolution, intelligently filling in the gaps that are created as it does.

Good ones do a decent job, but it's still won't actually increase the detail. Personally, I don't see a need for them if you have a good player already. DVD movies already look so great that it's a marginal improvement. If you were using a projector and screen though, then maybe look into it. Take a walk through a Best Buy, half of the players near me are all upconverting and are on display showing off what they got.