Our experience with cloud servers (gogrid, voxel) is I/O is the Achilles heel, hence if you're doing I/O intensive stuff like database batch processing or big queries (where not everything can be in memory in the same time) - you might be prone to issues. The lack of ability to guarantee I/O throughput means there are times that things will move a lot slower, and without digging in you sometimes won't even know the cause. We try to run all our DB servers on dedicated hardware because of that.