I definitely believe their are aliens out there ,even just our Galaxy(out of millions) is so vast it would be arrogant & narrow minded to believe we are alone.
The chances of us finding ET in the next 20yrs are slim, I only hope we find proof of ET in my lifetime.
As far as Intelligent ET's go I believe they will be found by a SETI project,however I think we will find very basic alien life much sooner with 1 of NASAs missions.
The benefits of finding ET would depened on how close they are to us & therefore how much communication we can have ,but their would certainly be pototential for different & more advanced technology to be exchanged as well as info & culture about their civilisation.
Possible dangers? Well I guess we could stumble across an ET version of the Nazis! But more likley is that some our religous extremist groups will cause some kind of trouble.
It would also be interesting to see what the various religions who believe we are alone would have to say about it & whether they would change their policy!
As for transmitting a signal ,too late we've been doing it for 40 odd yrs! I hope ET can distinguish between fiction & fact! ;)
I run S@H because I want to be part of the worlds greatest search & be able to say 1 day that I helped to find ET :).
I started S@H in 10/99 just trickling out the odd WU every day, shortly after I found out about teams for S@H & stumbled across Team ANANDTECH whilst visiting their forums. I found the people to be exceptionally friendly & helpful there in the Distributed Computing section. Also their is plenty of competition within Team ANANDTECH & I soon wound up my production & have never looked back ;).
So join us in The search!