Comment 126 for bug 548992

thijz: We have powersave enabled in the kernel by default. I don't know what kind of difference in battery life you'll see by disabling it, you'll just have to try it and see I guess.

Wireless powersave is a cooperative arrangement between the card and the AP, and it's known that some APs have problems with powersave mode that lead to dropped connections. If you only see this issue on one or a limited number of networks, it may be an AP problem, in which case it may be worth investigating whether a firmware update is available or if you can disable support in the AP. Otherwise I think that you can disable powersave permanently by adding a script to execute the iwconfig command in /etc/network/if-up.d (I haven't tested this myself though).