The following may just be my own personal experience with iCloud. Your experiences may differ.
Since I have been prompted, encouraged and enticed to dump MobileMe for iClould I have had a bit of a rough time of it.
for me iClould crashes frequently and in general has been a huge step backwards from MobileMe.
I understand product pivots and corporate changes of direction, these are business decisions that often push the envelope to good places. But when users are forced to become guniea pigs to the experiment I cease to be amused or appeased.
After I lose almost a hour each day just accessing and organizing my mail I begin to lose my sense of adventure. There is enough stuff that does not work in the diverse world of computing for the few things that did work begin to function inappropriately.
The big quandry for me is why in the heck it hangs up my whole computer causing me to perform a hard restart. I have tried iCloud with various browsers with the same result. I have not given up yet but my patience is wearing real thin.