Syncing is indeed important.

Managing properly thousands of feeds is a complex exercise that is probably out of scope for a desktop plugin and perhaps even to a whole mobile device. I would be happy if our preferred feed reader would handle efficiently the newbie case (discovering the potential of feeds) and the vast majority of users handling no more than 50 feeds (although some of them can be really noisy).

Still, imagine I could use tags to filter/promote entries to the desktop plugins e.g don't push entries with "Paris Hilton" or make sticky entries with "Maemo".

I also like Jaiku's principle of making easy to subscribe to a whole bunch of stuff and then be selective when unsubscribing (for instance unsubscribe to last.fm feed from my dearest colleagues).