Part of the reason to use Xwiki, especially, now that it has attachment versioning, is as a document repository.
Unfortunately, if you upload a file with a really long name, or one that has spaces in it, Xwiki will munge the name of the document. This does not happen on other Wikis (e.g. Confluence).
An improvement would be to allow documents to be uploaded with spaces or other special characters in the filename. This is not unprecedented as filenames with spaces are allowed in Windows, Unix, and MacOS. This way, if a user wanted to upload a file called "Marketing Report 2008-10-16.xls", it could be download by all members of the team without being changed (i.e. the actual filename is preserved). Maybe Xwiki could keep track of the real filename somewhere.