Like Bill mentioned, we read the forums as we're able, but you're always guaranteed a response if you send email to the
support ninjas.
The mail importer is based on Applescript, and is intended to handle attachments, but there are some conditions. The email must be sent as plain text, not HTML mail or some other text encoding which AppleScript can't process as well. (In other words, the app used to send the message can affect whether the info makes it to OmniFocus.)
I also heard some of the support ninjas discussing the possibility that the Snow Leopard version of Mail (unlike earlier versions) may not be including attachment information in the results that the script send back. I don't have more specifics than that, but if you send email and let them know what version(s) of Mac OS X your Mac(s) have installed, the folks that respond will have more info.