I have a CanoScan 4400F. Scans negs at 600 dpi/ppi. It has the plastic film/slide insert and it does a pretty good job ...
if you get the negatives inserted just right,
and you use get cardboard filler lined up just right. And it is slooow. Not counting the time it takes to tediously load the negative strip - 10 minutes to scan 4 frames and save them as TIF (if you didn't miss a fleck of dust on the strip, the platen or the cover that is...). It just plain requires way too much direct handling of the negatives in order to get a good scan.
It
is a good scanner as far as quality goes, and for slides it's probably well suited. And if you are in a clean room - and your negatives are perfectly flat and precision cut - and you've got lots and lots of time on your hands it's a great negative scanner too.
So to sum up, I'm shopping for a dedicated film scanner too. I see the Plustek 7200 & 7300 scanners which are in the price range I like. Are they any good? I can't justify spending $1K+ on a film scanner and I can't stomach replacing one migraine with another.