Thanks.
As the Apple-stated ram requirement (Leopard 512mb, Snow Leopard 1gb, Lion 2gb) increases with each upgrade, it's the potential for overall sluggishness and/or running out of memory when available ram is shared among other apps which bothers me - and moreso as mine is the earliest of the supported models, with less power and ram.
It's an issue I've noticed since upgrading to Lion from Snow Leopard, and don't want to further worsen things. (Years back, switching my then iMac to OS X from OS 9 was horrid - sure, it did all sorts of useful stuff, but overall it was much slower and frequently ran out of memory.)
As the Mountain Lion requirement of 2gb is the same as Lion, maybe things will be ok.