Researching more into social software, smartmobs, etc. has led me to some pretty cool (and in some cases totally unrelated!) sites:
Suprglu is a Digital Lifestyle Aggregator. The site collates the results of other social sites, such as Flickr, del.icio.us, etc. into a personalised homepage. Its use of RSS means you can also aggregate blogs, news sites, etc.
shadows.com A bit like del.icio.us, shadows.com offers a 'shadow' page behind a website whereby you can tag, review, rate and socially-link the site.
Etsy This online sale site (currently for handmade items only). Although not an auction site, it's being dubbed EBay 2 by some users. What makes it stand out though is not the business model, but the slick and innovative interface it uses. An an example, try searching for products by colour.