My little aggregator is 2 years old:
http://www.sexblogdemon.com/
It most important part is the intelligent java spider/bot. It has detection for rss feeded blogs and anti spam. It is now handling over 10.000 feeds and it still hosted on the thumblogger server, imagine that, i guess it can handle over 100.000 feeds with ease.
I must admit it seems to be a bit overkill to make such a big app, but i guess i had much time back in the days
