I'm still a bit at odds over ERD on OS X also. Shortly, XERD I think is good for small schemas with maybe less than a dozen entities. Past that and the inability to copy and paste entities bites. Data architect has a more complete package of things with it's domains, data types, and entities, but sadly kept crashing on me. I've become to not really care for Java whatsoever except on my cellular.
When I recently had to take my 12 entities in 3NF and normalize further to 4NF and modify the subsequent data model and application design, I didn't even bother with XERD or trying Data Architect again. I pushed through using scraps of paper and manually stroking the code together. However, after a couple of days, I realized the futility of such an endeavor and finally turned my PC on.
I really do try to do everything on my 12" PowerBook, but alas there's some things that it doesn't have. The two biggest at this point in time is TOAD and PowerDesigner as I work in an Oracle shop. I do have Virtual PC, but it's a beaten dog to run, hence the PC box.
Anyways, I'm using Sybase's PowerDesigner for conceptual and physical data modeling. It does basically everything I need it to do and more without too much effort. Simply put, it lets me concentrate on building what I want instead of what tool am I going to use to do it.
In the end, I've moved back to using a Windows tool to handle my database design. I'd prefer it to be an OS X one, but it ain't.
I wish you well in search. If DataArchitect doesn't crash frequently on you and offers the database support you need, then I think you'll have a good tool.