Well, I have one blog that's running on 99% sponsor RSS Feeds only (just a few handwritten posts) and it turns out pretty well for me. Definitely great for SE traffic, so definitely very useful for webmasters.
About surfers - well, like DJilla already said, they are really easy to use nowadays. I use Opera and even in that older version I'm using it already has a very easy to use built-in Feeds browser. So I'd say they'll get even more important as they already are soon and all sponsors who don't have them should go and add them in no time if they don't want to be a back number!
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