Solved my own problems (sort of)
Basically if you do a Response.Redirect(url, true) you'll always get an
threadabort exception from what I can tell. (the thread gets
aborted the moment the response is closed so anything past that line,
even a return; will get killed.
What was happening was that there was an image display ashx on the page
that was accidently closing the response. As soon as I took out
the close, the threadaborts went away.