I had a 6000L for more than a year, but I never used it much. I carried it with me, and it reminded me of appointments, but otherwise I simply did not make use of it to the extent I had used its predecessor, an HP 200LX.
I have now had a C1000 for two months, and I like it much better. The main difference is the keyboard, which I find much more usable, although not quite as good as the HP's. I also prefer the clamshell design, as I hardly ever want the keyboard and screen to be in the same plane.
Also, I can't count the 6000L's built-in wifi as an advantage. The no-name CF wifi card I use with the C1000 gives me much more range.
I wasn't interested in the other Cxx00 models, because of the microdrives.