I can confirm that the same thing has been happening to me for months now. I also use Linksys wireless-B, etc. Sometimes I can go on for an hour or two with no problem, sometimes in half an hour I lose the connection. So email cannot be sent and lots of other stuff get cut off in the middle. I "solve" it this way (a real nuisance): I unplug the power cord to the wireless unit and 20 to 30 seconds later I plug it back in. Then I have to click the browser to get re-connected. 90% of the time it will reconnect. Sometimes I have to repeat the process 2 to 3 times to get any result.
If there is a better way to solve this, I would be happy to know!