Thanks for all those responses guys esp. euphoricism
loved that line about the guys wife.

I have been running at 21 bb/100 for the last 9000 hands or so at microstakes(since I tried this 20bb. approach.) so even though it may not be optimal I will probably continue using that amount until I start losing.

I would start with a non-even amount as suggested but my approach is to always reload to 20bb's, so that I always have that amount pretty much before each hand and as soon as I have gone up to 40bb's I leave the table.

Miffed you said I'm playing too many hands, what would you suggest I do with PP's (66 & lower) in mid to late position in unraised pots with maybe 1 caller, limp, raise or fold?

K10 off-suit is the weakest hand I raise with & only then in mid to late position, should I add anymore?
My stats at the moment are about 25/10.

If I am re-raised pre-flop by somebody with a lower than 12 pfr %, I generally fold AJ & below & pocket pairs JJ & below is that ok?
I feel they know I've only got 15 bb's left so they expect me to call so even the microstakes players generally don't do it unless they have a top 10 hand.

I know that 4 a better player it is more profitable to buy in for a higher amount,
but for a weaker player I think this may be a decent approach.
I will keep you posted as to my results. Thanks.