I own a 50" Samsung DLP and I've been quite pleased with it. The HLP 4674 and its big brother, the 5674, have the HD2+ chip while the other models (the xx63 series) this year have the HD3 chip. IIRC, the biggest difference is that the HD2+ has better contrast ratio. I'd try to view them side by side to see if you can see a difference. These sets have a native resolution of 720p. The next generation sets will have 1080p, due out this year or early next year (if you believe manufacturers' estimates).

Make sure you watch the set for awhile and make sure you're not one of the people who see rainbows with this technology.

There's a ton of information on these sets over at AVS forum.