Nah, it'll be fine mate, I had a steel tank that had 2000psi in it for 3 years, it was only when I got it retested they emptied it and it passed with no problems.
If you have a slight leak! If you leave them pressurised it is better for the reg as it keeps every thing in place, I believe that you ar supposed to keep air in dive tanks (i.e. pressurised) while stored.