The original IBM ThinkPad, all the way back in 1992 or so, was a pen computer, and a tablet at that. Consumer tastes dictated a switch to a notebook convertible format, and pen computing historians may remember the ThinkPad 360PE and 750P, both notebooks that could also be used as tablets. For a good while there were no IBM Tablet PCs at all, but when the ThinkPad line became part of Lenovo, that changed again.
The Lenovo X220 was announced early 2011. It replaces the X200/X201 that goes back to September, 2008, and that machine was a replacement of the earlier X61. The concept of all those hybrid Thinkpads hasn't really changed in a long while (though the original models in the 90s did use a different display conversion mechanism), and the machine itself still looks like ThinkPads have always looked: black, elegant, businesslike and angular. It's just that technology doesn't stand still, and so IBM and then Lenovo have been providing regular tech updates and inclusion of the latest and greatest standards and features.
So what's new this time? Well, Intel has upped the ante once again with its first and second gen Core i3/i5/i7 processors with integrated graphics and turbo boost and all the good stuff. So in addition to a 2.7GHz Core i7-620M, which is already last year's news, the X220 can be ordered with the second gen "Sandy Bridge" Core i7-2620M (2.7GHz, up to 3.4GHz in Turbo Mode), the Core i5-2620M (2.5GHz, up to 3.2GHz), or the low-end Core i3-2310M (2.1GHz, no Turbo Mode). All of the new chips have a Thermal Design Power of 35 watts, use speedy DDR3-1066/1333MHz memory, and include Intel's latest advancements and also faster graphics, so it's not quite clear why the "old" i7-620M is even included. However, unlike the X200 that had an ultra low power processor option (the 1.2GHz Core 2 Duo SU9300), all of the new chips are quite powerful.
Disk technology hasn't been standing still either, and so you can now get higher capacity disks both at 5400 rpm and 7200 rpm speeds (and some offer a degree of full disk encryption). Further, with solid state disks now much more affordable, you can order the X220 with 160GB of SATA SSD.
Despite the speedy processor lineup, Lenovo quotes exceptional battery life. Up to 9 hours with a 6-cell battery, and up to a stunning 18 hours with the 6-cell battery and the ThinkPad external battery pack.
One thing that Lenovo keeps changing are display size, aspect ratio, resolution and display technologies. While the old X61 offered a standard 12.1-inch XGA (1024 x 768 pixel) version and a high resolution SXGA+ (1400 x 1050 pixel) version, the more recent X200/201 switched to WXGA (1280 x 800 pixel) resolution, still 12.1-inch, and electromagnetic digitizers. That's now changed again, and the new X220 has a 12.5-inch display with 1366 x 768 resolution that's wider yet. That's what 720P HDTVs have, and it's a good format for watching HD video. As before, there is a base display and then an outdoor-viewable version that comes with Corning's virtually scratch/break-proof Gorilla Glass. And there's a nice 720p webcam.
On the digitizer side, multi-touch has become pretty much mandatory even though, in all honesty, it doesn't do that much (yet) on a Windows machine. But the X220 has it, and it even works in conjunction with an active pen.
One flaw in the design remains: still no integrated optical drive. Others have shown that it can be done even in ultra-portable machines. As is, if you need an optical drive it's either an external plug-in drive or Lenovo's ThinkPad X220 UltraBase. The slot situation has changed yet again, with the base machine having a simple SDHC card slot, though a 4-in-1 card reader is supposed to be available. There's now a Display Port jack in addition to VGA, there's still an ExpressCard slot I believe, and you get fingerprint scanning.
On the wireless side, there are numerous options and variations. There are three variety's of Intel's Centrino WiFi module, with one even including WiMAX. You can get Gobi 3000 for total technology and carrier independence, or there are a variety of 3/3.5G WLAN cards.
Pricing starts at US$1,199. That's a US$300 price premium over the plain vanilla non-tablet X220, so there's that to consider. Yes, Windows 7 supports touch and multi-touch, sort of. But it's still a mouse OS. If you can live with that, the X200, like almost all ThinkPads before it, is a classy, and likely very dependable machine.
Update May 2013: the X220t was replaced by the X230t, which is largely a tech update (see Lenovo webpage).