Google is experimenting with tremendously many new gadgets. Many of them go public, and you grow to like them, then suddenly they are axed. Remember Google Answers, where you could pay real human experts to answer the questions? Or the SOAP API? Or one of the not-so-few other services that went down?
[Update 05/08/2010]: The very hyped Wave collaboration service will also be going down.
Well, now there is help available for you to judge what Google services will be available in the future. In its AdSense permission guidelines, Google metriculously gives a listing of its trademarks. My thinking now is that if they care enough to put a service (or its mark) in this list, they care enough to continue the tool.