I've had the same problem. Maybe KGet is not closing file descriptors and eventually hits a quota limit or something? For me the problem shows itself by KGet, after having downloaded some files, getting stuck on the same file that it downloads over and over again. The workaround is the reboot.
I just updated to KDE 3.2 and KGet got worse. Now it disappears from the system tray after partially downloading the first few few of a bag of files and obviously downloading stops.
My system system is SuSE9+kernel2.6.1 with KDE3.2 from SuSE's website.
Thank you for the hint on how to disable KGet. I'll do that to hopefully get rid of the annoying popup about KGet not responding every time I reboot.