Thanks, this looks helpful for Mac users.
I did some more sleuthing for Windows users like myself, and it looks like there are a few options that aren't quite what I was looking for, but are close:
Shell Tools
http://www.moonsoftware.com/shelltools.aspRelevant feature: "File note", which creates a txt file with duplicate file name for entering in comments.
TagFolder
http://virtual-protect.com/tagfolder.aspxFeatures a Windows Explorer shell extension that lets you right click--->tagfolder--->assign tags. Only supported on 32 bit systems.
Elyse
http://silkwoodsoftware.com/index.htmlFeatures an external file manager system based on tagging. Not quite what I was looking for, that is, a tag/comment option that is "sticky" to the file, but maybe this works for some people.
The -wallet=<name> option looks promising, especially if there's an equivalent GUI option (eventually) that eliminates the need to search %APPDATA% and start messing around with renaming wallet.dat's. I think Armory at least lets you add a brief "nickname" tag to a particular wallet.dat, whilst in the Armory GUI. It certainly isn't a critical issue, but in the spirit of making the original bitcoin wallet grandma friendly I think it would be a big step. I know I've already corrupted a few (empty) wallets by accidentally renaming them while bitcoin qt was running. D'oh!