Submit bugs here: https://github.com/bitcoin/bitcoin/issues
Although all of the GUI code is being replaced in the next version, so don't bother submitting UI bugs.
RE: debugging what bitcoin is doing in the 10 minutes it takes for the window to come up:
tail -f ~/.bitcoin/debug.log
... should tell you what it is busy doing. Probably loading the block chain and reading the wallet (do you have a very large wallet.dat?)