do user_scans and no user_seeks mean the index is useless? I'm digging into sys.dm_db_index_usage_stats and finding that a number of our indexes are used exclusively in user_scans, not user_seeks.  Does this imply that the index is useless and should be redesigned?

Thanks!
Not useless, but maybe sub-optimal.  Scanning a 10 MB index is a hell of a lot faster than scanning a 1 GB table, though a seek would be even better.  Can you tell us more about the indices?  How are the tables being used?