A couple months ago, I made a Titanium app as part of the interview process for my current employer. The app is B2B, not available through the store, so I will try to compensate below.
The app appears non-trivial to the user. There is a QR code reader that takes snapshots of industrial equipment, saves the URLs to a local database, long-polls the URLs to continually display fancy gauges that mirror actual hardware output in real time, and pops up service information when equipment stops running.
Performance-wise, the app is laggy but the lagginess is perceptually the same as similar well-established native apps. All QR/barcode scanners are slow and all data access over wireless is slow so what if Titanium tacks on an extra second or two. (I don't have any benchmarks either way, it could be the same for all I know).
To explain, I believe it's an established fact that to the end user, anything under 2 seconds is "fast" and anything over is "slow". There is no differentiation.
Productivity-wise, the app took 2 full days and several evenings to develop. For reference, my programming background is: web development - advanced, javascript - fair but hardly advanced, mobile - zero, stateful/compiled/memory managed applications - zero. As you can imagine, Titanium takes all the credit.
My overall impression is that Titanium is the right tool for the right job (horrible documentation notwithstanding). The lack of "awesome" apps is probably because it's not right for games and hardware-centered apps. To put things in perspective, I am a medium-heavy app consumer and for me personally, games and hardware-centered apps comprise maybe 25% of what's in my iPhone and iPad. That leaves a whole lot of applications that could easily be done with Titanium.
Go to the Apple's marketplace right now and filter out all the games. Then filter out all the apps where the app is just a thin frame for the content (I say that because I am pretty sure you wouldn't notice if Titanium was used in place of native, because of the 1-to-1 API to native UI). I bet you are going to feel that there are very few awesome showcase apps left there too. That's just the nature of the beast.