There was an issue with the EU gingerbread update (The people who got updated early).
I'm unsure if this issue was fixed with the UK roll out but I don't think so.
Essentially they set the wifi to d/c if the signal strengh dropped below -88db (I think). As far as I have been made aware this is a perfectly use-able signal strengh so I don't know why they have set it to this.
I have to smoke outside, I often sit in the shed which was way out of wifi range. So I bought a repeater. Still the signal drops all the time. I have like 4 out of 5 bars on the wifi icon, then suddenly it just drops to no signal and 5 - 10 seconds later it's back again. If I use my laptop I have no problems at all
To be honest it doesnt effect me browsing, but I can't youtube as everytime the signal drops the video fails to play and I have to restart it.
If your phone is rooted you can fix this. The code is highlighted on XDA , they also have a custom rom with the fix in place.
Obviously you can't root the IS without a hardware mod as far as I am aware. Bit of a bummer as HTC have now agreed not to lock their boot loader. Typical that I buy the only HTC that you can't root - Clever....
I don't see HTC fixing this in a hurry. Would be simple enough to do another OTA update. To be honest it should of been fixed before we recieved our update, I presumed this was the cause of the massive delay in getting the update to the UK. Many people informed HTC of the error , then they stopped the update for about 2 weeks, the update finally came through and it doesn't seem that they have fixed it.
Turning mobile data off simple stops the wifi from d/c'ing completely and using 3g instead, it does not fix the issue, wifi still drops and you still need to wait for signal strengh to increase.
I'm going to complain about this to HTC now. Basically I'm going to go down the road of , My phone is "unuseable" , either fix it or replace it. Something like that.
I'll be back
-Deano