It's not a biggie as such, but it could be... I actually lost both of the 2 screws on my Xpt (don't know how, as I've never took them off myself), which resulted in the nut not staying completely still, which in turn over time resulted in problems in tuning stability.

Guitars: Ibanez SV5470F, Ibanez Xpt700, Fender MIM Standard Stratocaster ('04-'05), Jackson Ps-2
Ashton AG200,
Amps: ENGL E530, Bugera 6262-212,
FX: TC Electronics G-major 2, Behringer EQ700, Morley Volume / Wah