Apple recently introduced a sub $1k iBook so I've (almost) promptly put my Vaio on eBay. Now this doesn't bode well for my emotional state as this will be the fifth laptop I've purchased in the last two years.
Initially I purchased a 12" Powerbook to replace a tiny 300 MHz, 12" ThinkPad. In all honesty I should've stopped there. Instead I got kind of nuts when I saw the Powerbook could almost play Warcraft III, so quickly returned it for a more powerfull 15" Powerbook.
I loved that 15". But ultimately I stopped carrying it around often enough to justify owning a laptop because it was so heavy. Around then I discovered the Sharp Zaurus C860, and believed it to be capable of replacing a notebook. It wasn't; it did have the battery-life of a laptop (doh!), but the Arm processor made it difficult to find / compile software for it. In retrospect I wish I had tried distcc before I sold it. It is possible that had I been more knowlegable about Linux I could've made it work, but I doubt it -- there were a lot of issues with the various distributions (1, 2, 3) available mostly relating to yet-unsupported hardware and software unavailability.
Next I purchased a Sony Vaio Picturebook. Now I had always wanted one of these -- I'm a huge fan of ultra-small laptops; the screen runs at 1024x480, for example. And generally speaking I was very pleased with it. In my sheltered Mac days I had assumed that Linux, since it is virtually ready for prime-time on the desktop, could also be almost as effective on a mobile device.
Linux on laptops sucks. Although, to be fair, I'm dying to see how it performs on very supported hardware (as opposed to average hardware --there's a company that sells laptops and desktop as well as offering their own Linux distro in an attempt to bring the Mac experience to Linux, but I couldn't find a link). And, again to be fair, my Picturebook's hardware is all fully supported except for some ACPI closed-bios issues (that are Sony and Microsoft's fault). Because Sony implemented Microsoft's implementation of ACPI instead of the standard, Linux is having some trouble with power-management, specifically suspend. Although Linux's power-management in general needs a lot of work, I was able to get suspend-to-disk working with the 2.6.7 kernel which made things a lot nicer.
To sum up: Desktop Linux works very well because your computer never goes anywhere, so you've got the time to get working whatever you need it to do, and it stays working. But when you're mobile and run into unexpected situations such as needing TV-or-VGA-out, strict wireless LAN requirements you've really got a know your stuff, and it will still take a while to set up.
So I'll be getting a 12" iBook. It's not a desktop replacement or for gaming, my Linux desktop works very well for that. I'm sure it will be fast-enough for my mobile needs, and it's a Mac so it will just work, even in unexpected situations.