The creators of Urban Rivals, an app that is based on a virtual trading card game, have let us know that they too plan to go the free-with-microtransactions model as soon as their app is released, and though we haven't actually heard from Tapulous, Andrew Lacy told us outright that the only reason Tap Tap Revenge 3 had a 99 cent price tag on it was because of Apple's limitation, so we'll expect that app to go free as soon as it can.
Clearly, there's a drive for this model on the developer side, but the question will be just how much this echoes with consumers -- certainly the "download a trial, buy more later" model has worked well on other platforms, so we can expect it to work here on the App Store as well. But on the other hand, just as when the App Store first opened for business, it's a very "wild west" moment -- everybody and their brother is offering up in-app transactions, and they're all of varying prices and quality.
My guess is that we'll see a few "hits" -- a few free apps that everybody buys content for (Tap Tap Revenge 3 is a good guess; considering that because you know most of those songs, there's much less guessing on what the quality of the transactions will give you). At the same time, there will likely be apps that everyone agrees aren't worth the in-app purchase (it's the old story of "horse armor" when Xbox Live started doing microtransactions). Until we find a good balance, where quality meets price, odds are that it'll be tough for consumers to know just what's worth it, and thus tough for developers to convince them that their content is.