When I've played with aggregating various folks' info some things have been easy - snag their homepage, autodiscover (or scrape) the location of their feed. Snag their FOAF. Snag their friend's feeds. Rinse, repeat.
But I hit a practical block when it came to the other stuff, not helped by personal mental blocks. The practical block was that very few people include references to their other web-attention stuff : del.icio.us, flickr etc. The personal mental blocks were firstly that I hadn't bothered to read the FOAF spec in a long time, forgotten it really does have proper support for this kind of stuff. The second personal was I haven't bothered to update my own profile for a couple of years. Get to the point you boring git...thank God it's Friday (and every day is a cat photo day!!)
So anyhow, I bet the SemWikis can do this better, but in liue-e liue-ay of that, here's a page called LazyFoaf on the ESW Wiki. Please add your bits (and please tweak as needed to make it easy-scrapable). If there's somewhere else already doing this, please point me.@en