My (lousy) experience with moving PIM (personal information manager) type data (tasks, notes, calendar, address book) from Outlook/Palm to MobileMe(ss), OmniFocus, Evernote and Remember The Milk have given me that lonely pioneer feeling. I'm even starting to miss my old Nemesis.
I feel the jaws of the Data Lack trap ...
Every method of selling software has its own Dark Side.
Microsoft's traditional model favored proprietary data formats (Data Lock), feature mania until competition died, then forced obsolescence every 2-3 years.
Ad-supported software has to get us to look at the ads. If we stop looking, it will get more and more obnoxious. Data Lock helps ensure we can't escape, even as the pain level rises.
Software as a service has technical issues (Gmail was down a few days ago - again), but, above all, Data Lock is a terribly strong temptation. At least on the desktop there are local files that conversion software might run against.
...while all three models suffer the Data Lock temptation, it's strongest in the "Software as Service" model...
I'm not completely alone though. Google not only supports Document Freedom Day, they've made some real moves towards data freedom. There's DataPortability.org, the cryptic microformats initiative, and good old OPML.
We need to push the "cloud" vendors towards the world of data freedom, or they'll make us nostalgic for the lost tyranny of Microsoft.
Update 5/15/10: Happily, we now have Google's Data Liberation Front. I have issues with Google, but the DLF is one reason they are lesser of all evils.