The thing that really gets me with all this real-time hype is people attribute the rise of Twitter to all the awesome desktop clients built for it so you can receive your tweets in real-time, the problem is they aren't actually real-time, all those desktop clients use polling, just with a really short interval.
If you really wanted your desktop RSS reader to be just as awesome and real-time as Twhirl then just set all the feed refresh intervals to 5 minutes, no RSSCloud needed.
Having done almost this exact thing, the issue is that 4 out of 5 large websites will have blocked you buy your fifth poll for abusing their service.
I always thought that it was somewhat ironic that nobody had a problem with me refreshing slashdot.org every 10 seconds trying to get a first post, but that they had a very large problem when my rss poll hit them more than once an hour (is at least what their recommended interval used to be.)
I was going to mention this but I decided it wasn't really necessary to make my point. I was just trying to show that no matter how hard certain people push real-time it usually still comes down to polling in a desktop situation. I think people have gotten it into their minds that 15-60 minutes delayed isn't real-time while 1-15 minutes is.
But I agree that most places will throttle you if you request their feed too often, so how are they going to feel when every one of their subscribers requests their feed within the same minute every time they make an update? I guess that's the big question.
If you really wanted your desktop RSS reader to be just as awesome and real-time as Twhirl then just set all the feed refresh intervals to 5 minutes, no RSSCloud needed.