Installed it several days ago, ran fine. Converted books, downloaded rss feeds, loved it.
Yesterday I installed Python 2.5 to run the ereader2html.py script, calibre would hang on start up, take up 175MB + of RAM and 100% CPU. Uninstalled Python, still the same. Uninstalled calibre, rebooted, reinstalled, same thing. Deleted all temp files, uninstalled, rebooted, ran a registry cleaner, reinstalled, same thing.
Command line tools and LRF viewer still work.
This is on Windows XP Pro, SP3.