You may be interested in these two iPad apps that give you a way to
use TiddlyWiki in your DropBox:
http://itunes.apple.com/us/app/twedit/id409607956?mt=8
http://itunes.apple.com/us/app/tiddlynotes/id465930290?mt=8
Otherwise, as Hans says, you can straightforwardly get a read-only
view of TiddlyWiki files in your DropBox.
TiddlyWiki5 will indeed soon give a lot more flexibility in terms of
letting you store tiddlers as individual files in your dropbox, but
it's not yet in a usable state for end users.
Best wishes
Jeremy