When I post my rss feed with an invitation to subscribe I figure that may get subscribers but is is also counted as a backlink?
Not sure I understand your question so I'll answer from both ends - Posting an RSS feed on your site doesn't give you a back link but if you convince a person who is in a complementary niche to put your RSS feed (with anchor text to subscribe) on their site then it is a backlink - but only if you are using anchor text with your site name/url. Those who do subscribe don't give you backlinks. However, if you burn your feed through Feedburner (owned by Google now) they may be weighting the number of subscribers in their algorithm in the coming months. Hope that helps - Gail