According to the changelog, the Dropbox iOS app v3.3 also gained several under the hood improvements, including smarter caching and bug fixes.
But the important change today is the improved search and document previews. The app now enables users to search for and preview any Word document, PowerPoint presentation, or PDF in their Dropbox account. This saves users from having to open a document in another app (an office app, perhaps). For example, a user can view, scroll, and zoom in on their travel docs without needing to switch out of the Dropbox app.
You can find the app in iTunes.