I am sure that y'all have seen this many times ... you want to check in at a venue and there are numerous duplicates, misnamed, or inappropriate duplicates.

To help clean up foursquare, you can go to the Get Satisfaction forums and post the venue information that needs to be corrected, merged into the real venue, or simply deleted.

As a guide on the correct manner by which you should post the information, simply look at other posts in the thread and mimic how others are composing their replies.

For Eastern US States: http://getsatisfaction.com/foursquare/topics/eastern_us_main_thread_for_merges_edits

For Western US States: http://getsatisfaction.com/foursquare/topics/western_us_main_thread_for_merges_edits

For all other locations: http://getsatisfaction.com/foursquare/ideas/recent (pick the appropriate link based on your location)

A caveat:
If you are unsure, ask. the SUs on the forum will help you / answer your questions