Users of FeedDemon on Windows and NetNewsWire on the Mac using Newsgator synchronisation have a month (until the end of August) to update your software and migrate your OPML feed list to Google Reader. Alternatively you could find some other means to manage your feeds. For help on transferring your feed list to Google Reader, check out the instructions here.
Personally, I use the client tools across all three of the supported platforms, Windows, Mac OSX and iPhone. I'm hoping that the transition to Google Reader will "just work".