So... here's my take;
"A Person is smart, people are dumb" (MIB)
There are a few apps that already have in-app purchasing and the reaction from the users, at least in the reviews is not one of acceptance. I think this won't really change much of anything in the App store. Sure there will be more apps with in-app purchasing (IAP) but will we see a ton of free apps that allow you to actually try out the app then use IAP to "activate" the full version? I really don't think so.
When I'm reviewing an app in the iTunes store I check to see how much the apps costs, what it does, who makes it and what else they have made. I also checkout the developers web site and hope there is some type of video demoing the app. With IAP I won't know the ultimate cost of the app unless someone mentions it (either the Developer or a reviewer). In addition, will this put an end to yo-yo pricing changes struggling developers do for attention? If you don't know about this it is very common for an app to start at a price but then go up or down, sometimes to free to stimulate sales. I understand it but it ticks me off if I just paid $2 for an app and now it's free!
We also don't know how Apple is going to track these new FAFBWIAP (Free At First But With In App Purchasing) apps. We can assume they are still going to be listed under the initial free category; if so you can expect a lot more of those useless reviews.
It will prove to be interesting indeed.
Update: I released two games, one for iPhone and one for iPad and just for the reasons listed above I also released separate Lite (free) apps. This limits the number of di#$ward, butthole reviews you get and keeps them in the free version where quite frankly who cares, the app is free if it looks interesting you're gonna try it regardless of the reviews.