I have the same problem with my Linksys BEFSR41 v3 running v1.05.00 fw.
Internet can be fine for days on end, then just drop. I usually just hit the main power on the wall outlet off for 30 secs, turn it all back on, wait another 30 seconds for all the lights on the modem and router to steady. Job done...!!! Works fine after that.
Bloody annoying having to do that thou........