Just thought that it was worth mentioning that the startup time of Calibre has dramatically improved for me going from around 3-5 minutes to less than 10 seconds with the move to 0.7.30 and then 0.7.31 on Windows 7 Pro. This is a huge improvement
I run with quite a large library (~11000 books) and have that located on a NAS so I am guessing that the change to caching cover information that is mentioned in the Release notes has done this. Thought that it was worth pointing out that in my environment the gain was much larger than I had expected from posts I had seen earlier in the forum.
Calibre generally feels snappier as well although that may be my imagination as I have not done scientific measurements elsewhere.