Had the same story from the engineer who fitted mine in November. Had spent quite a lot of his time changing modems due to the overheating issues.
I did ask the stupid question "I guess mine is the newer one then???" - he replied "yes", with a wry grin!
And just to add, my Infintiy has been stable now for longer than any of my other connections, and the speed is great. Only issues have been when there has been "engineering work" posted on the BT site for the night before, and these have sorted themsleves out after a day.
1999 Freeserve Dial up --> Freeserve Anytime ---> 2005 Wanadoo 512k BB ---> Jul 2009 Orange up 8 Megs(hah!) --> Nov 2009 O2 LLU -> Nov 2011 BT Infinity( getting 37.5 megs now on ethernet)
Yamaha AW16G user