I got a big improvement in Wifi performance just by moving the wifi access point to a slightly different location and setting the antenna on it at about 45 degrees to vertical when it was previously vertical.

Prior to that performance was patchy even at times when the indicated signal strength was reasonably good. Radio is strange stuff...

It is true (as mentioned above) that wifi equipment shouldn't be near cordless phones or their base stations, or you'll get interference, which shows up as poor performance.

Anahata