There's a new 'stats' button in HubMed search results that provides an improved graph of occurrences of query terms in MEDLINE abstracts over time, plus an analysis of the most frequent authors of papers matching the query terms (only using a sample of 500 papers for the sake of speed, but it should still be useful).
GoPubMed's HotTopic section has some very nice statistics for analysis of papers and authors matching queries for Gene Ontology terms.
Update: added graphs of co-authorship, using YAPGVB. Again, this is limited to a sample of 500 papers and a minimum of 2 co-authorships.