Thought I caught me a spam bot. Or maybe not.
The IP Addresses (80.58.5*.*) of the spammed referers all point to proxycache.rima-tde.net. When checking my logfile there seems to be 1(!) legitimate request on there. A google search with the name of a classmate of mine. A rather unique name I might mention.
Now I looked up that domain with google and spam and what turns up: an old thread at Webmasterworld about this domain.
So either this bot is very clever, which is still my guess because it only requests a couple of pages and no stylesheets et al, or there is someone really weird out there surfing my homepage. I am still banning all those referers and probably the IP-Addresses as well if more of these turn up.