The best way to try out Spark & related tools is to follow the 2 days exercises from the AMP Camp 3, they have a script to launch the whole cluster (Berkeley Data Analytics Stack) on ec2 very easily so you can get your feet wet without too much effort.
I helped write the AMPCamp exercises (and parts of Spark) - the exercises were done in the context of a two-day long seminar held at Berkeley where the days were mostly filled with talks/training about the stack. The actual exercises were designed to take a couple of hours each day, with plenty of time for questions/etc. You can probably get through them in an evening, and I've seen people do it in less!