New builds at:
http://download.calibre-ebook.com/betas/
Changes:
1) Check Book now checks CSS as well, in stylesheets and inside <style> tags
2) Renamed Tweak Book to Edit Book. I think I found and changed all references, but if you spot any old references to tweaking, let me know
3) Updates last_modified and filesize automatically when launched from inside calibre
4) Various small bug fixes for issues reported in this thread