My Magento website is pretty fast. Pages are loading within 2 a 3 seconds. I'm using the compiler, and APC caching.
Also my checkout is fast, except when it's loading the shipping costs. I'm disabled all shipping methods to check if it's due to a plugin. But still, when I disabled everything, loading the shipping methods is very slow.
Especially /saveBilling is slow (1.3 minute). Strange thing is that it was fast before and I didn't did anything.
I think I have a good Blackfire profile now. Generating this profile took me about 1.42 minutes. The other profiles were pretty fast, so nothing was wrong with that I think.