Lo, and the cries of the Mac Blackberry faithful went up, and indeed they were a fractious multitude: "Where is our dial-up networking?" they wailed. "We are paying for data service on these things, and it's EVDO, and everyone else is doing it!" And they saw that those with Intel Macs could tether their Blackberries within Parallels or VMware, and did get online after a fashion, but they said "This is a silly hack, not good." And they saw that Pulse would give them a proxy server and Bluetooth, but they cried "This is slow, and we crave USB!"
And the developers of iMobimac did hear this loud kvetching, and did indeed release upon the multitudes a private beta of a new, USB-based DUN tool. No way to gauge final performance yet, and the beta release notes warn that Safari may not detect the proxy server running on your machine, but it's a start. You may sign up for the beta at the iMobimac site, and may the broadband be with you.