#1
right im gonna be really breif,
I have an ibanez and its not that old, its in brilliant condition appart from the fact that when i tune my guitar ( drop tunings ) my what would be the G string wont tune perfectly and is slightly out of tune, no matter what even when turning the tuning peg it won't tune into the perfect key.

fellow rockers (: what the hell do i do ?
#2
New nut, if that doesn't solve it new tuners.
Or you could buy different strings with a wound G string, that would solve it too.
#3
lubricating the contact points between the guitar and string could help to some degree, also new nut/tuners could fix it if yours are really bad.
#4
Did you set the intonation? Tune the strings to pitch like you want them, now fret the string at the 12th fret. Using a tuner, is the string at the 12th fret the same as the open string? If not you need to adjust the intonation

ESP LTD RZK-600
4 Custom Strats
1 Custom Soloist (Warmoth)
1 Custom Telecaster (Warmoth)
2007 Jimmie Vaughan Sig Strat

Callaham Hardware & Bridges
Fender Custom Shop 69's
Dimarzio Breed Pickups

Blues Junior Amp
BlackStar HT Club 40 Amp
#6
I have always had good luck with Grover tuners, I would recommend them.
***Guitars***
Epiphone Les Paul Custom AP (w/ 2 Seymour Duncans)
Jackson Dx10D Dinky (w/ DiMarzio PAF Bridge)
Epihpone Hummingbird

***Amps***
Marshall JCM 2000 DSL 100 (Voodoo Modified)
Custom 4x12 Halfstack (w/ Veteran 30's)