I find it fairly unlikely that the legendary (in Red Hat, Linux and GNOME circles anyway) Havoc Pennington is going to read my blog, but over in his latest entry Log for December, 2005 he mentions the need to replace his X-series ThinkPad.
Like Havoc, I've noticed that the rate of progress in laptop design appears to have slowed – the current ThinkPads are not massively different to those that were around, say, 2 years ago, although you generally get more bells-and-whistles such as the funky fingerprint readers and hard disk "airbags". Personally, I think the T-series ThinkPads are impossible to beat. Perfect combination of svelte design and power. I always long for a laptop with a higher memory capacity, of course… my work T40 is ageing somewhat and I'd love to break the 2Gb barrier with my next machine, along with a disk larger than 80Gb. On the other hand you do pay a bit more for the T-series range. Well worth it, in my opinion.
If you are thinking of running Linux on your ThinkPad, don't forget the awesome ThinkPad Configuration Tool for Linux, the Linux on ThinkPads mailing list, and the ThinkPad section of the Linux on Laptops website. Oh, and I ought to add that although I work for IBM, I don't endorse either of these sites in any official capacity – my opinions on these things are entirely my own.