There are a ton of videos of Apps on YouTube now. It's a good way to check out an App before buying.
I really hope they add trial versions in the future because its really needed. For example, I would like to get an app to track my mileage and calculate my average MPG for me and there are like 5 apps that do that but I'm not sure which to buy.
We don't even need trails at this point but trailers for the games, like with the movies section.
Some games screen shots don't tell the story of the game. Like with De Blob it looks boring with the screens but the game is actually fun, I had to wait until Touch Arcade posted a video of the game before I bought it.
Nothing stopping the developers from creating limited feature demos in the free app store...