Well, I finally mustered the courage to install ML (August 28th release) on to my 550D/T2i.
I followed the preparation/installation instructions exactly but when I attempt to update the firmware I get a brief flash of a loading screen, screen goes blank and the card access light just sits there flashing, slowly, approx. once every 3-4 seconds.
I left this for approx. 30 seconds but then panic started to set in (heart rate increased significantly with the thought of being the first "genuine" case of bricking my baby  ), so switched off and popped the battery out.
No damage done (heart rate returned to normal  ) but I was wondering, how long should this process take?
Did I panic too soon?

If anyone who has installed ML could tell me how long it should take, I would be very grateful.

If it makes any kind of difference, I'm using a Transcend 16Gb Class 10 card.

Thanks for the response a1ex.

Strange thing is, I am already up to date with Canon firmware, version 1.0.9.

That's the version that the camera was supplied with.

 
I can't believe I didn't notice that.

Thanks a1ex, ML installed and working nicely.

try running the T2i EOS utility on the desktop and updating the firmware again?  I had the same problem as Tichro so I went and did the same thing.  I'd guess the EOS utility should be able to install over it...

sorry for bringing back an old topic!  but i did find this thread useful.