It is 2400x4800 DPI.
I'd recommend, as this is a scanner, to buy whichever model at Best Buy and pay the $30 or whatever for the extended warranty. I did for my HP scanners and, as a result, got $400 in credit - which I applied to the new Epson scanner and an upgraded video card. :9
http://reviews.cnet.com/Epson_Perfection_2400_Photo/4505-3136_7-20077919.html?tag=pdtl-listhttp://reviews.cnet.com/Epson_Perfection_3170/4505-3136_7-30527152.html?tag=pdtl-listCnet and zdnet had virtually identical reviews, including ratings (7.2 and 7.5 respectively). Amusingly, user comments differ on both sites. I don't understand why users reported the 3170 so badly. (The negative comments have no commonalities amongst them. If lots of users report the same problem, then it's time to raise your eyebrow. And as for the user who whined about OCR quality, OCR software that's bundles is crap for any brand and I've used many. Only ABBYY FineReader does a decent job at OCR...) The 2400 also appears omre highly rated because it's an older model and has been out for some time. The 3170 is comparatively new.
http://reviews-zdnet.com.com/Epson_Perfection_2400_Photo/4505-3136_16-20077919.htmlhttp://reviews-zdnet.com.com/Epson_Perfection_3170/4505-3136_16-30527152.html?tag=pdtl-listZdnet claimed that bright colors lacked saturation.
Zdnet's big complaint on the 3170 is slow speed for higher optical resolution. All I can say to that is "Well, duh" - higher resolution takes more time and is worth it. They also nitpicked the included s/w package, but Adobe Photoshop Elements 2 is a good product, I bought that separately some time ago for $100...
But if you can spare that $40, the extra resolution and ease of use with scanning negs is well worth it. (3200x6400 makes a gigantic difference in quality.)