Some great counterarguments by Marco Arment on the (annual) debate on App Store free trials.
Personally, I think that free trials would help the sales of apps priced at $9.99 and above. While it's true that we, as geeks, tend to try as many apps as possible, I admit that I would feel uncomfortable with spending $40 on four apps that may not even be what I'm looking for. But I also agree that trials may create new problems for the "middle class" of apps that get tried but not bought. It's a difficult problem to solve. Surely Apple must have better data and insight to corroborate whatever decision they'll end up making.
From Marco's post, I'd also highlight this footnote:
Abolishing the “top” lists from all App Store interfaces and exclusively showing editorially selected apps in browsing screens would do a hell of a lot more than trials to promote healthy app economics and the creation of high-quality software.