3GS Wifi connection drop-outs

I've had my iPhone for about a month, and all has been well until this last week.

For some reason the iPhone is now not recognising my home wifi, or my works wifi. Previously it would log on automatically.

At home I have noticed, under General/WiFi, that it seems to be searching for wireless networks for about 10 minutes without finding any. Previously it would pick up about 6 networks (mine and my neighbours) in about 30 seconds.
The other problem is that it may have established a connection, then a while later again loose it. I've noticed this because I can be using the web, then wonder why it's suddenly so slow.

The only way to solve either of these problems is to turn the phone off, then on again (I didn't think this was a Windows device!)

Is anyone else having similar problems?

I suppose I will have to go back to the Apple store to see what can be done.

As a slight aside, I have also noticed that while the phone is asleep it doesn't respond to the home button, I have to press it quite a few times.

The phone is in great condition and hasn't been dropped etc.

Anyway, would be good to hear from others who have had / are having the same Wifi problem.