Stumbled onto this site quite recently as I was looking for a counterpart to imdb.
This site is good for gathering together all the movies that you have seen, and creating a list of the movies that you would like to see. You can also import the movies that you've rated from imdb.com.
Currently, it's kind of devoid of activity; the discussion groups are lifeless, and I don't think that there are very many members just yet. There are membership options, but they seem useless as of now. The search function also needs a little tweaking - it can be unreliable sometimes.
With some more attention, icheckmovies.com could be very good.