I have a BeBook and I haven't regretted the purchase for a second. The support-team is very responsive, and it's a great device. Especially the fact that it supports folders (multi-dir) and many formats (ePub, PDF, doc, PPT, LIT, .......)
Mobipocket should be available really soon, although I (obviously) don't know when... but it won't be long
I use a Mac myself, and it works fine with the BeBook.
If you should have any questions about this device, don't hesitate to ask them!