It seems that along with Referer spamming, SMB spamming, and all the old fashioned manifestations of this vile practice, we now have blogdex spamming. It looks like it's something akin to google bombing.
The blogdex front page currently contains many entries like PremiumDomains - www.pornovideo.bz - DOMAINS FOR SALE and so on. Looking at the track page it seems that 8 sites in the ubiquitous.nu domain have been registered with blogdex and are successfully bombing it. Raph is going to have a field day