I started off my small hardware obsession with a Libretto 110ct. (I had the Sharp 5000D and 5500 earlier, but they were more of a curiosity than really useful for me )
I got a Libretto 50m because I hated the trackpoint on the libretto, but the lack of cardbus made it impossible to put USB on it.
Loving the touchscreen, I upgraded to a Panasonic Toughbook CF-1, which has cardbus, USB, and a touchscreen, all in a nice magnesium case. It remains the single most solidly built laptop I've ever seen. (I've seen 2 or 3 stories about these machines stopping bullets!) It definitely sacrifices the size aspect though - small as it is, it sure *isn't* a Libby.
Told the Panasonic with me to Japan and got an 860. Never looked back, really, even though the 860 lacked the HD and USB host.
I've gone through a 3000 since, and I currently use a 3100, and there is no comparison to the Libby. The 3x00 will basically do pretty much anything that can be done on one of the old-style "VHS" Libbys. The newer ones are a different matter, but even then they aren't really the same.
The U100, I dearly want to get my hands on, though