So I don't use an aggregator, here are my reasons.
I tried out Radio, but I found it awkward - I couldn't figure out how to update my feeds without reconfiguring Radio's update time to a minute from the current time. Radio runs a desktop server (yuck) which updates feeds once per hour, but like most Net users worldwide, I'm behind a single phone line with per-minute fees (albeit very low, less than $1/hour) for staying online, so I'd much rather have something I can fire up to grab the latest stuff whenever I go online.
Fine, I'm sure other aggregators would be fine for this, but the other problem I have is that I almost always read everything on my blog list anyway. I have a dozen blogs in a Mozilla Tab group which I read every morning, and I always read through all of the posts, even if I only skim some. If I aggregated these, I'm sure I would first read the summaries, then read all the posts, so I would only be adding to the time I spend in my morning blog reading routine.
Now that I think about it, it might be useful to aggregate my second and third tier blogs, the ones I read when I'm bored, waiting for things to compile/download, etc. Generally when I decide to check out one of these I read the whole thing then too, but if I had summaries of all of their content, I might spot them talking about something especially relevant to me right now, that would otherwise scroll off into their archives. I'll chew on this.
The other thing on my list of things I'll never have time to do is to play with the idea of aggregating into my blog pages. That is, it might be neat to list the headlines of posts on some of my favorite blogs in my sidebar or somewhere similar, sort of a super-blogroll.