Blue smoke means burning oil. Now this is most likely to come from worn piston rings. It could also be due to worn valve guides, this would be more noticeable on startup.
When your car overheated there is a likelyhood that it could have slightly damaged the rings (guides are less likely to be affected IMO.)
Check that you're not losing lots of oil.
check at least weekly.
keep an eye on coolant and oil and your car should run nicely.
If it passes MOT (on emissions) and isn't using too much oil or creating a smoke screen I'd basically ignore it. Getting someone to remove the pistons to renew rings is likely to cost more than the car is worth.
S
STeven
February 2010