I am not sure that the basic iCloud Photo Stream will be all that useful for the volumes of data that enthusiast and pro photographers generate. It still has to transfer over the same network that everything else does ... moving a 16G card's worth of image files is going to take forever no matter what over wireless service is.
Nor do I really want all my photos to be streamed hither and yon over wireless to all devices ... I configure each specific device for specific duties, depending upon its features and capacities for intended work, and don't put everything I've got on each of them.
I suspect that there will be apps written to the iCloud APIs that will do the job better, with more sensible configuration for us "power users". That's the real key to iCloud: the API suite that allows it to be used as an integrated part of an application's data storage workflow.
We'll see what it does and where it goes when it ships...