At first I thought that the site was censored because maybe somebody has published some pictures that could have been considered offensive for the UAE as a state or for their religion. But I noticed that YouTube on the contrary was freely accessible and this was a bit of a contradiction. I discovered that Last.fm was censored but the Italian channel Lastfm.it was not (and that definitely should have been an oversight for them).
I asked some locals (foreigners living there, not real Emirati) about that and they told me that Social Networking sites were in general looked unfavourably. Only recently the access to some of the most important sites, Facebook to start with, was unblocked. Apparently from a technical point of view the censorship can be easily avoided (I don't say if through the use of an external, free DNS system, or through some HTTP tunneling service; I didn't care to check): for the less experts there are some small computer shops in Abu Dhabi where you can go and ask to have your PC configured to avoid the block.
Social Networking sites aside another block was on Skype as you can see from the following image.
This has probably less to do with politics and more with economy: in the UAE there is a semi monopolistic Telco named Etisalat which is surely making huge amount of money from international calls: just consider in fact that 81% of the residents in the UAE are not Emirati! Last day I was there I read on a newspaper that apparently the Communication Authority of UAE requested a formal Telco license to allow Skype to operate. Anyway you can't access the Skype site but you can use the program if you have it already installed on your system. In this case you cannot recharge your credit to call international "standard" phone numbers.
Back in Italy I've noticed that ThePirateBay site is still inaccessible from Telecom Italia ADSL networks. This is what you get when you enter the site URL: