Earlier today, I saw a lazy web post about using mod_rewrite to redirect pages if you change your MT URLs. Check out Generating MT Entry Redirects.
Another thought that I had today — if you are moving a blog from one location to another (think changing domains), you could use a redirect right in the Individual Archives on the old server through MT before deleting the old blog.
Example: (in the head of an Individual Archive template)
<meta http-equiv="Refresh" content="1;url=http://your-new-site.com/archives/<$MTEntryID pad="1"$>.html">
As long as you are using the same naming scheme with the MTEntryID (which is the default), your old entries will point directly to the new site.
After a while, once people have stopped linking to the old domain, then you could just delete the individual archive files from the old server.