I always find when I bring my guitar into the pub from the car that the strings tend to be a little sharp rather than flat.

The other thing is that sometimes you find in a noisy session that you are hammering away, and when you check the tuning it's gone up rather than down. I assume all this is something to do with changes of temperature or humidity.

On the other hand when I take an instrument up at home which I haven't played for some time the strings tend to be a little flat. So I don't think there is too much to worry about instruments getting sharper and sharper till they explode...