Well well well...
I'm not going to act like an Apple fan and deny that there are any faults with my device, no matter how many times I have to do a hard reset or take it to an Apple store for repair (this happens a lot, both the faults and the denial).
My Galaxy S2 is fu**ed!
Last Thursday, I took it out of my pocket to find it had zero signal. Being on O2, I had the same issue last year when the network went down so called them. They said there were no reported problems.
I tried my SIM in a different handset and sure enough, full signal. I then tried a friend's O2 SIM in my S2 and nothing.
Called my insurers who said that my phone was still under warranty with Samsung (at that point I wondered why I'd bothered taking out insurance. 2 year contract, 2 year warranty. Anyway...)
I phoned Samsung who went through the steps you'd expect, including the ones already suggested by O2 and eventually told me to back it up and do a factory reset. I've done this now and it's still no use.
Sooo, off to the repair centre it goes, once the courier gets in touch, that is. Should be repaired / replaced and returned to me for free, provided they accept it's not my fault!
It's 18 months old now but still, you expect your phone to see out it's contract!
On a side note, I had a quick look at the htc One and Sony Xperia Z in Carphone Warehouse the other day, they seem HUGE compared to what I'm used to.