How do you track your RSS subscriptions? I've been wondering about that recently. I didn't want to use Feedburner since you have it give it control of everything.
I log requests for my feeds and count the unique IPs from them. This isn't quite accurate though, since it'll count one person from multiple places. I suppose a better solution is to point my RSS subscription link to a redirect page which logs the subscription request. However, I don't know you'd miss anyone who somehow subscribes from the straight link to the XML feed.