...hmm I'm a little worried my PS3 might be about to die and its trying to tell me its in trouble. Recently almost every other time I turn it on it beeps and goes through the video output selection thing (the bit where you confirm you want it use HDMI etc)... is there a fault with the system? or am I looking at a dodgy HDMI cable? Or is my OS3 just very forgetful and doesn't remember its meant to be outputting via HDMI... 
 
Cheers for your help people!

Moving to the PlayStation 3 forum.

Have you tried using the PS3 through a VGA cable yet?

Sounds to me like a bad connection somewhere.
 
If you switch to RGB/SCART and then plug your HDMI back in, then this happens. The fact that your HDMI cable works at all suggests that the problem is in the box, maybe around the HDMI output itself.
 
If you have time maybe you could back up your saves and do a format/reinstall and see if that fixes the problem. Otherwise I'd say get on the phone to Sony.

damn I don't really want to have to send it off, I'm far too attached to my PS3 for any kind of time away from it... 
 
I'll try the RGB thing, I've just taken the cable out of both ends and given the ports a little brushing to get rid of any dust that might have infiltrated the socket...

Switch your HDMI cable out for a new one as it might be faulty. This happens to me after I've unplugged the cable to the PS3. Don't worry, your PS3 is not about to die.