Hi,
It also depends on from what perspective you are looking at it. As nihil said from a buisness point of view it can allow a company a better IT platform than they could normally invest in. Of course, once you dont have total control of your enviroment you are giving up security but while I wouldnt say it comes down to trust, you do have SLA's and contracts which can limit the risks.
The biggest secuirty risk from cloud systems is when employees use "FREE" cloud services. As was pointed out in a security seminar i went to, if a company is not making money selling you a service they are making it selling you.
Muracu