try to copy all the files after you complete a fsck on that partition/hard disk
after this you could try cleaning the hard disk with a low level format tool provided by the manufacturer, possibly samsung, if you know the brand of the hard disk, visit their website, these tools provided by the manufacturer will also diagnose physical errors on the hard disk and other details
if the tool reports errors, time to replace the hard disk, if not, just format it again with ext3 or ext4
for low level format you can also use dban http://www.dban.org/
if you see repeated errors after all this steps the error could involve problems in the hard disk controller or mechanical failures and that is a reason to change the hard disk
"Is a new high-level format from either the PCLOS installer sufficient, or should I use a different tool?"
on linux i always used the tool that comes with the distro, after almost 4 years on pclinux and other 2 years with mandriva i can say that the tool used here is perfect for my requirements
about rebooting, is the machine always on? if that is the case, not much people leave a laptop on that long time but shouldn't be a problem afik if you do it correctly(by asking it to reboot and not doing a hard reboot)
"And one last question; is it worthwhile to attempt to upgrade to the existing KDE4.3 now or just wait until the PCLOS2010 comes out?"
i did it last october, all ok here but pclinux 2010 with kde4.4 is the future here, literally, you will need to format your installation and use the new version
no update path exist to avoid broken installations so you could consider to wait 1 - 2 months or try the new desktop but sounds more easy to you the wait option isn't?