Prasad,
Well the economics of demand and supply is coming in your way, as companies are in a major hiring mode, candidates are ensuring they make hay when the sun is shining, one of the fallout i personally have seen is the increasing number of "no shows", most active job seekers are essentially looking to either renegotiate their terms at their current organisation or fishing for a bigger catch, unless the candidate is "really" interested in your offer and organisation, they will most likely go back to their current firm and check for hike by showing or hinting of your offer OR keep looking out till they find a fatter pay packet.
Well, if you do all the things correctly, such as selling the "worK', highlighting the "pay" ( matching expectation ) , show their "path" in the organisation, extend a " genuine warm" welcome and do a good follow up, the chances are that you may have person on board. Make sure you are consistent in your mails with the individual thru the notice period and extend all courtesies to check if they would need any support joining your organisation. Do not count on candidates as "filled" post offer, the actual job of recruting in today's competitive market is a good follow thru. Remember there are tons of companies out there looking for these same folks.
Good luck...