The redirection solution I’ll use when I get around to fixing my archive permalinks comes from Elizabeth Lawley. (Shelley has some notes as well.) Clever stuff. MTEntryID needs padding, though, and Shelley’s quotes got smartened. Word to the wise.
Mark Pilgrim has tips on archive names, which are pretty good even if I don’t mind having .php on the tail of each URL. Which I don’t. But the keywords trick will be very useful, since my post titles tend to be cryptic.