No, I'm not thinking about Google Docs & Spreadsheets or even web-OSs. I'm thinking about pretty simpler things such e-mails, bookmarks, notepads...
The problem is when you have/want to use two or more computers (exempli gratia desktop/laptop) and feel at home (sync!) with both of them.
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Yes, gmail is fine, but what about offline e-mail reading? Making it available the IMAP protocol would be great. But it seems there are technical- or will-hurdles since it is the most requested feature for gmail and nevertheless there are no clues that it will be introduced... Actually it's now a long time since I start using gmail, but still I can not feel myself satisfied.
For scratch notes, I just started to use Google Notebook, but, again, there is the offline problem. So I think I will resort to some poor-man text-file scratches to be kept sync with Unison.
Concerning bookmarks, I tried Google Browser Sync (yes, always and ever Google...), but I'm unable to make it work correctly with bookmarks: it starts syncing but then it pipes up that I exploited too much traffic and then stop syncing (maybe I have too much bookmarks, grown day by day by means of a store'n'forget mechanism...). So I had to resort to specific tools such the Bookmarks online Firefox extension, but one has to remember to manually upload/download... and in the right time-order! In fact, if you forget to upload your changes from one PC just before going to use the other, you are going to be hoist with your own petard. And twice: you can not both enjoy the last changes (since they're not in the web-service database) nor upload new changes (otherwise, when you are supposed to download them on the first PC, you will lose the change made on that first PC). Thankfully, I mainly use desktop-PC during the week, at work, and laptop during w-e, at home, so it is supposed to be easy to remember of uploading/downloading at the right time...
Moreover, my bookmarks have an additional issue, since they also keep the feeds for my Sage rss reader (absolutely the best ever feed-reader, IMHO). When I switch to my laptop after a week on my PC and I check my feeds, mostly all of them will be shown as "to be read" even if I already read them on the PC. I was supposed to solve this problem with Google Browser Sync, since it can sync also the history of the browser. However, even if the single piece of news of each site is correctly recognized to be "visited", the site itself continues to be shown as "unread".
Yes, really a big mess. :(