Now that I regularly use an aggregator I've found they're great for personal blogs but not for everything. Many sites just have lousy feeds: Daily Python URL and Fucked Company (via newsisfree) are both content-free. Gametab also doesn't syndicate enough content; kind of a special case since Gametab is itself an aggregator. Yahoo's most emailed contains too much new stuff and isn't sorted: I only want the top 10 items a day.
The more vexing problem are Slashdot and Metafilter. The aggregator experience is impoverished. The strong design is lost in an aggregator. And the comments that make both sites so interesting don't come through at all.