Okay, I'm a former Xperia X1 owner and I would NOT recommend the phone to others.
Good points are pretty much what Gorskar said.
The screen is recessed so it can be awkward to hit the Close/OK button in the top right and the Win button on the top left. I've been through 4 of these phones and they all had LED bleed and clouding from the top corners as if the screen was tightened down too much. The colour tones and automatic brightness are very good though, as is the 800x480 rez of the screen. It's just a shame the screen is smaller than some comparable WinMo phones.
The camera is adequate, but if you're looking for a "proper" cameraphone, you'd be looking at something like the SE C905 or another of SE's Cybershot range. It does have autofocus and geotagging which is nice if you upload the pics to Picasa and see where in the world they were taken.
Panels. Sorry, but I consider this to be a total waste of time. It doesn't bring anything unique to the phone and while it can be handy to have a panel for media, a panel for FM radio, a panel for Facebook etc, the whole interface and switching time is SLOOOOOOWWWW.
The arc-slider is indeed a nice piece of engineering and is very positive in it's action. I personally felt that there was too much "give" in the screen when shut. You could visibly press the screen section closer to the keyboard section.
The speaker volume is quieter and more tinny than I hoped for, but definitely usable for a conference call or while watching a video/Youtube. Videos will need to be converted to play smoothly on the X1 and there is an application on XDA-Dev that you can use for this specific purpose. It was designed for the Touch HD, but since the basic hardware is essentially the same, it works for the X1 as well.
While these niggles collectively might colour my opinion, there is one thing that I simply will not accept and that is poor build quality. That is the case with the housing of the X1. Each of my phones suffered a crack in the casing underneath the battery cover, near the volume button. My most recent phone cracked underneath the battery cover halfway down the side, and also had two cracks in the silver bezel that goes around the outside edge of the phone. I'd never dropped it. This was from being either in my pocket or in the car mount performing satnav.
That was my third phone and I've given up on the Xperia. Instead of performing a doorstep swapout replacement (refurbished models), I opted for an insurance claim so that I got a brand new handset. So I now have a brand new handset that I'm preparing to put on eBay. All I have done is open the box to turn it on, test the functions and update to the latest generic ROM (R3A).
Manufacturing date: 09W17
If despite my little rant you're still interested in the X1, I can let this one go for £250. I appreciate that you can take your chance on eBay and get one for a lower price, but all I will say is that this particular handset *IS* a brand-new insurance replacement. While I'm new to this particular forum, I've got a "senior member" rating on XDA-Dev and I'm also Paypal verified. As you can tell, I've been honest about my reasons for wanting to sell this handset.
I'm looking to get a HTC Magic for my wife as she's fallen in love with it and this sale is to help finance that purchase.