I'd certainly like to see a "file browser" where someone can pick previously uploaded files out from a list box with some directory navigation links as part of the new entry form.

This would get translated into a file name and file size as defined by a required MT template. Something like:
<img src="icon.gif"><b><$MTUploadFileName$></b> (<$MTUploadFileSize$>)
could get added into any of your entry templates with <$MTEntryUploads$> or something similar.

As it is, once the anchor is copied into the new entry, if it is accidentally edited or deleted, there's no way to get it back without knowing exactly where that file was uploaded. This would make it easier to post several files at once in one post (using a multi-select list box) or in multiple posts (by FTPing a bunch of files first, then picking them out one at a time when creating new entries).