Jepsam - I just happen to have printed a list of extensions NOT to touch are:
.386, .bat, .cat, .cmd, .com, .cpl, .dat, .dll, .drv, .exe, .hta, .htc, .inf, .ini, .lnk, .msc, .ocx, .pif, .sys, .vxd, zero-byte .log files, and files without extensions, like hosts.
I usually don't delete anything I can't figure out from reading it. You'd be surprised how many you can get rid of that way. It may have an abbreviated word from a web site you deleted or the name of a .jpg file you're familiar with or an e-mail attachment. Just back up what ever you delete with the date.