Hi anshita_sayal -- very good questions!
If you're definitely planning on applying for bschool after a few years in the workforce, then many would recommend taking the GMAT now, while you're still in school -- and still in study-mode. The test score is good for 5 years. The one downside is that the percentile rankings do change from year to year. So, if someone scored, say, a 45 on the quant when he tested in 2010, that was in the 74th percentile that year. The same score is only in the 71st percentile this year, because more test-takers have gotten stronger scores on the quant side in the last year. So that's a small risk, but it may not be a big enough risk to forego taking the test now when your skills are probably strongest.
The other issue that you raise is the fact that the GMAT is changing. They are adding a new section to the test, and they're also removing a piece (one of the two AWA essays is going away). So you're right, this could also change how the percentiles might play out among future groups of test-takers. The core quant/verbal are not changing, as far as we know, and the scoring will stay the same overall (we think). Either way, the schools will have guidance in terms of how to evaluate new test results versus old results, so the timing of the test's changes should not really be a factor for anyone in terms of when they decide to test. The advantage to testing now would only be that you have the full history of the existing test on your side; it's more of an unknown in terms of how to prepare for the new version etc., though BTG is certainly the right place to be to learn about these things as they come out!!!
Best of luck!
EssaySnark