I'm guessing the recent comments widget is just doing an ORDER BY date DESC LIMIT 10 or something? With an index on date, I don't see how this could be slow.
Appears that he has 188590 rows. It definitely sounds like a configuration issue. Maybe the mysql table cache might be bogged down or the query cache is full or malfunctioning. Could be a lot of things.
Sorting that into a temp table, and caching that in memory would be really fast on a server with reasonable RAM and proper indexes.
How long does the query take?
How many rows do you have?