I've signed up because a colleague wanted to use it as an example for some work I'm doing. So far, the UI is just grim. Here's a list of issues as I find them...

• Why on earth do they need my date of birth? What are they going to do with this information? They don't explain why they need it, and they don't give me the option of not answering. Consequently, I lied.
• Search by High School/College/whatever. Clicking on a link opens a new window!! Is this the 20th Century? Am I using Netscape Navigator 3.0? No!
• Search by High School asks me what country I live in, with options like 'England', 'Scotland' and 'Wales'. Hello? What happened to the United Kingdom? Did these US wankers just decree its dissolution? That pisses me off.
• Having searched for my former "High School" (or as we call it "school") classmates, what happens? It doesn't work - I just get plonked straight back where I started: "Find your friends on Facebook." I'm using the latest stable Safari - what "Web 2.0" developers don't bother to test on a Mac?
• OK, let's see if we have better luck with "College" (or as we call it "university")...
• ...No let's talk about that localisation first. They've gone to all the trouble of cutting my country up into dozens of little parts (right down to 'Isle of Man' and 'Channel Isles') but they can't be bothered to make a localised version of the site? Hang on let me check... Right, I've changed "country" to "England" in my profile, and now it says England is my "Hometown" (note, that's oneword), but it still hasn't changed any of the UI option accordingly. I've tried other countries, but as far as I can tell, you can have Facebook in any language as long as it's US English.

Don't I have anything nice to say? Well, some of the UI features are quite nice.

• Some of the search boxes have auto-completion, which works smoothly and well. Not all of them though, which seems odd.
• The "Add a Friend" dialogue pops up inside the page, and then fades away once you're done. Nice.
• The draggable profile elements is nice, but over-sold. The two-column layout seems fixed - all I can do is choose the order of (some of the) elements.
• The search filters don't seem to work very well. I'm looking for my friend John Smith (not his real name) but there are a million of those, so I filtered on "male" and "ages 24-35". Result? No hits! Not one! I suspect that SQL query needs looking at...
• I take it back, the searching is rubbish. I've just searched my friend Paul Scott (actually his real name). The vast majority of hits are people called "Paul Scott ?Something?". Why on earth do they think I'd type in someone's first and middle names??? And I can't even filter by COUNTRY!