depends on manufacturer really. they have so many ways to rate monitors nowadays it's hard to go by specs personally i bought a 19" 4ms from sony and returned it the next day b/c ghosting was very apparent. then bought a 24" 16ms from Dell. BF2, WoW, L2, CS, Doom3. no ghosting whatsoever.
so if you really looking for an LCD, i recommend choosing your LCD based on personal reviews from other people, or if possible, personal experimentation.
Like Nubius said the rating is really over rated. Ive never seen my dads 12ms screen ghost yet ive seen this 17" Dell CRT (that im on now, not mine) ghost horribly.