@sachin: I use a few 3rd party programs on the iphone (for multitasking, for allowing skype over 3G, etc) and with one of them you can 'pull' a small drawer on top of the screen with a bunch of toggles (they're customizable). I have the following toggles set on mine:
Cellular, 3G, WIFI, Bluetooth, GPS, Brightness..

In my daily usecase I use wifi at home and at work and I generally toggle wifi on only when I enter those two areas. It's very quick to do... turn on the phone, swipe the lock, swipe down for drawer and there's one-click access for all the toggles I mentioned above.

For 'saved' access points, it will auto-connect without any prompts (you'll see the 3G icon replaced with the WIFI 'fan' icon).

Want me to take a short video (<1 minute) to show you around?
Won't hurt to see what the competition's like. Heh.