ok, i've been living with this for long enough, and it's starting to piss me off...
i've got a palm tx running vanilla kubuntu kernel 2.6.15 (though the problem has been here through earlier kernels as well). initially, when i boot the system, the palm connects fine (that is, i can connect it after a fresh reboot--doesn't have to be connected on boot).
if i disconnect the device, and then try to reconnect, nothing happens. no dmesg output, no syslog. the "lightning bolt" over the battery meter doesn't appear on the palm, although the palm beeps when it's connected. the only way i can get it to reconnect is to restart the system, which is annoying.

lsusb also shows nothing. any ideas?

When it does connect is it being mounted so you can access its files or memory cards? It sounds like what happens if a mounted medium is removed without first being unmounted.

no, this is a palm tx--doesn't mount like the lifedrives do. i think i figured it out though (at least how to fix). looks like you need to disconnect the device, rmmod ohci_hcd, then modprobe ohci-hcd and reconnect. i've been trying to figure this out for almost a year. hopefully that helps someone. a couple of other tips for palm connection...

using kpilot, it seems that if the kpilot daemon attempts to "listen" before the hotsync on the palm is pressed, it doesn't sync (same behavior with jpilot). solution is to hit sync on the palm before opening kpilot. otherwise, open settings, change device location (eg /dev/ttyUSB1), then hit ok after hitting sync button on palm. if anyone has a cleaner solution, lmk.
ymmv.