1. Go to settings and turn Wi-Fi Off.
2. Open your favorite Terminal Emulator App and type the following:
> su - > cd /data/misc/wifi > calibrator set nvs_mac wl1271-nvs-calibrated.bin xx:xx:xx:xx:xx:xx > cd /
3. Go back to settings and turn Wi-Fi On again.
Why would you want to do this?
Well if you, like me, have two HTC Desire V's and you have made a CWM backup of one of them and restored it on the other - to save yourself the hassle of having to set everything up the way you want twice - you will probably find that you two phones now have the same Wi-Fi MAC address, and thus that your router will be assigning the same IP-address to them.