I collect RSS aggregators like some folks collect stamps. I (obviously) don't do this for practical reasons. Realistically, no one really needs an aggregator (though if you're an avid reader of weblogs they're pretty much essential for keeping things manageable.) Anyway, I've got a ton of them.
An extended ramble on tools, aggregation, and people who you should probably be tired of by now.
I have so many of them, not because I've found any real problems with my main aggregator (NetNewsWire Lite) -- it's a polished product that keeps getting better. Rather, the thing that drives me to try all of these aggregators is to appreciate (with sheer, geeky wonder) the number of different approaches that developers have taken to deal with the aggregation phenomenon. One of the chief questions has been how to keep feeds synchronized if you read them from a number of different locations. One approach is to run the aggregator as a backend app using web front end. This is the approach taken by Amphetadesk and (so I hear, though I've never used it) Radio Userland. If you have your desktop machine aggregating this way, then, in theory, you can poke a hole in your firewall and read your feeds by connecting back to your desktop machine even when you're sitting offsite. A related approach (used by Blagg and its descendants) is to batch up a number of feeds and hand them off to another application for display/postprocessing -- you can integrate Blagg with LiveJournal or a MovableType installation (or a Blosxom installation, or course), for example.
Another approach is to transform the RSS into a non-web-based format, like email (example: fetchrss) or Usenet-style newsfeeds (example: nntp/rss.) If you're the sort of person who spends all day in your email client or newsreader, his has the advantage of allowing you to read all your feeds in that same environment, and even lets you take advantage of all of the advanced filtering and sorting (procmail, gnus) techniques that have evolved over the course of decades around these venerable technologies.
Though I am not a programmer, I find it fun (yeah, I'm nuts, aren't I) to play around with all of the programming and scripting environments available on OS X. This "playing" basically means installing the development / runtime environment and a few useful(?) applications to go with it. Because of it's not-like-anything-else nature and cruddy memory/process management, the classic Mac OS was often locked out of these environments.. OS X has dramatically changed the playing field. Right now I have tools/utilities/toys (some of which I use every day for real stuff) written in Perl, PHP, Python, Java, Ruby, awk, Smalltalk, shell scripts, and probably a couple I'm forgetting. Most of the environments didn't even exist on Macs prior to OS X, or existed only in severely compromised form (Perl, Java.) Folks have implemented a dizzying array of blogging, aggregation, content conversion, and wiki-ish tools with every permutation of these tools.
Personally, I find the technical end of the whole "blogging revolution" (ack, p-tooie) much more fascinating than the endless "a-list" navel-gazing (which Sven pillories and which some anonymous funny person satirizes.)
“I may appear to be just sitting here like a bucket of tapioca, but don’t
let appearances fool you. I’m approaching old age … at the speed of light.”
— Prof. Cosmo Fishhawk