Of the many book cataloguing and reviewing sites that are around, I use (and love) LibraryThing and GoodReads. LibraryThing satisfies my dorkish love of lists, statistics and free books; GoodReads is great for posting updates on your reading, bookish discussions.
LibraryThing is also brilliant for events and the whole sense of bookish community - you can nosy at other people's virtual bookshelves that are similar to your own, learn all kinds of facts about your own libraries (e.g. how high your books would reach if stacked up - mine's somewhere in between Stonehenge and Cleopatra's Needle...) AND, importantly for this post, participate in bookish events, both real and virtual.
If you fancy curling up in the sun (or hiding from the rain, if you happen to also be afflicted by living in Yorkshire!) and doing nothing but reading, there is a LibraryThing ReadaThing event scheduled for the 6th and 7th August 2011! Lots of people doing a lot of reading - perfect!
The 6th also happens to be 'Do Nothing But Read Day', which is handy!
To get more information, check out LibraryThing's ReadAThing blog here - you can sign up for the whole weekend, just Do Nothing But Read Day or just a wee hour here or there. Just don't blame me when you get caught up in the list-making wonderfulness that is LibraryThing (which just so happens to be free, did I mention that...?)