I'm aware of the couple "searching for a wildcard tag gives you a blank page" bug reports here, but wanted to report that if you search for a wildcard tag, it now works, BUT if you try to add a second tag to that search, it fails miserably with a proper (non-blank) 400 error. This is particularly bad, given that you explicitly link to the pages that give the 400 error after a search for a wildcard tag.
To reproduce, merely click any of the "related tags" links below:
hxxp://stackoverflow.com/questions/tagged/python~
(and for some reason, the system won't auto-link that, and it thinks that my htmlifying of it means I'm posting two hyperlinks)