This method grows in popularity every year. It has pretty much made the Grand Slam Force obsolete. (It used to be that 5NT asked partner to bid a grand slam with 2 of the top 3 honors, but in the days of RKC, that method is no longer needed).
Since 5NT is almost never a contract you want to play in, bids of 5NT are used as artificial and say: "Partner, I'd like to be in a small slam, but I am not sure which one--you choose."
This tool can be useful on many auctions, for example, consider that responder holds:
K 5 4
K J 8
A K 10 7 2
His partner opens 1 and he answers 2.
Opener rebids 2NT. Now what?
Responder is not interested in 7 (with 18 opposite maybe 13), but probably is willing to play a small slam.
But which one? He could belong in 6 if opener holds: Q J 4 3
Q 10 7 2
Q J 3
Opposite: K 8 3
A Q J
Q 10 7 6 4
, the right contract is 6.
And, facing: K Q 3
Q J 3
A 6 4 2
Q 5 4
6NT is where you belong.
In all cases above, over the 5NT "pick-a-slam" there is a good chance that opener would indeed pick the right slam.
There is some judgment involved in when to make the 5NT bid and how to respond to it. The responder should take into account the previous bidding and try to make an intelligent decision (no snide remarks or thoughts about your partner, please).
Is 5NT always "pick-a-slam?" Pretty much -- especially as a jump. Of course, 5NT after a 4NT ace-ask is still asking for kings.
Note: The auction 1NT-5NT has always meant: "Bid 7 with a maximum." This is a strange form of quantitative! I can see an accident happening if one partner thinks it invites 7, but the other thinks it is a modern "pick-a-slam" bid (maybe something like: A10
. This is not something most partnerships would discuss, and I can't say for sure which is the better agreement to have.
According to ACBL, no bids on the 4-level or higher after the first round of the auction are alertable.
updated: June, 2012