Hi Milind,
Just to clarify what you're asking about - it sounds like your concern is that you might see some of the questions that appear on the 4 GMAC practice CATs in these Forums. Seeing those questions BEFORE taking those CATs would 'spoil' each of those CATs and you'll end up with a practice score that is not realistic.
If that is what you're concerned about, then you are RIGHT to be concerned. As such, you should avoid any question that's been "tagged" as an Official GMAC question (until you've taken the 4 GMAC CATs or until you decide to 'research' any particular questions that you've seen on one of those CATs).
Since there are 4 of them, you should space them out during your study schedule, along with any other CATs that you might take. There's something to be said for saving at least one of those CATs until the latter part of your studies, but there are enough quality CATs on the market, that you have options even if you "run out" of Official CATs.
How long have you been studying?
Have you taken any of those CATs yet?
When are you planning to take the GMAT?
GMAT assassins aren't born, they're made,
Rich