Ah. Not sure. My sync with MobileMe doesn't take nearly that long, unless I have a lot of zip files built up over the weekend. Even then, I have only a random few times seen the iPhone act like you describe. I have never seen the Mac act like you describe.
There are a lot of factors in play here such as network speed and distance to the MobileMe server housing your account. Not sure if a different WebDAV solution would be any better or not. Have you tried signing up for the Omni Sync Server beta to try that out?
http://www.omnigroup.com/sync/