hey JunkyJohn,
I don't have a Treo of any kind yet, but I have a Mac running OSX. I'm looking for a smartphone to replace my Palm m515 and my mobile phone. So far for a Mac compatibable unit, Palm is the only thing I've found. I'm just waiting for awhile to see if any other mobile companies will carry it, as I'm thinking of jumping from Sprint. Also, as you've read in the forums, there seems to be many issues to be ironed out as yet on the 650.
I use Filemaker Pro for my business and keep several databases on my laptop. I can sync them to my handheld's FilemakerMobile application. It works great. As for syncing with Mac OSX native applications, I just found this software called missing sync. here's the website. I think this is what you'll need.
http://www.markspace.com/missingsync_palmos.php
Good luck and let me know how it works out.
Mikey :D