They definitely need to launch the paid version, but I wouldn't worry too much about your files getting lost. Pretty much by definition you should always have at least one backup of your files. Worst case and they close tomorrow, you still have all your stuff.
Update: They already have paid plans, $99/year for 50GB.
Re:Rands in Repose Gives Dropbox Love
by sreitshamer on Wednesday November 26, 2008 @01:34PM
(#377898)
Only the latest versions of my stuff, that I haven't deleted. Previous versions and deleted files are only on their servers.
"Dropbox reserves the right to terminate Free Accounts at any time, with or without notice. Without limiting the generality of the foregoing, if a Free Account is inactive for ninety (90) days, then Dropbox may delete any or all of Your Files without providing additional notice."
And I can't find the actual pricing for non-free accounts anywhere on the site, which isn't increasing my trust level.