I was taught years ago to cache encryption keys for as short a time as possible. It seems to me that the window of opportunity for this mischief is very small indeed - the attacker needs to get physical access (basically, steal the laptop) and perform their voodoo straight away - say in a van parked right outside - and that's going to be expensive. Or they'd have to get to your desktop while you're out of the office - but if they can do that, they can install a keylogger and audio bug anyway.

And one minute to get to the memory? It takes me longer than that to put the laptop in the carry case.

Of course, physical security underpins data security every time, so if you are serious about encryption, keep your laptop on you or locked away - that really goes without saying.

The TPM aspect may change things, but since I don't use one, I can't really say.