If the cloud computing providers you are considering provide a good service then they should have a number of case studies listed on their website. If you are in any doubt about their credentials and you are considering investing time and money in their services then why not contact some of the case study clients, preferably ones based in your own country, to hear their opinion first-hand? Search the internet for any reviews, too. You cannot stop customers from blogging or tweeting when they have something to complain about!