I think that syncing the pim's around my Ubuntu landscape is a missing feature. All kinds of Calendar software like Evolution, Kontact or Thunderbird (with lightning) are able to sync. It is only a small step to finish this issue, i think. It is possible to stream music with Ubuntu One, but no sync with local Calendars or Mobiles. I think that the pim syncing feature is more important an useful as the music streaming one. I only get an account on Ubuntu one for pim syncing and mobile sync option. Right now Ubuntu one closed this feature. For what really I should keep this? For music streaming?
You see that Apple opened a iCloud solution for their mobile and clients, too. Why does Ubuntu closed their most useful option?
If you say that i can use Ubuntu one as a backup system for my Ubuntu files, another third party companies do this work better.
But if Ubuntu were able to does backup data and pim data, yes i think there are many people, who want pay for this option without asking, like me.