Ever wish you could try out a paid iPhone app before you bought it? You may be able to soon! Apple recently sent an email to developers stating in-app purchases would be allowed in free apps. While the structure will vary by application, this means that developers will be able to release a free version of their application, and later charge more for a premium download including more content or features.
The only downside I can think of is that this may encourage developers who would have released free applications to begin to charge for premium content. The upside: you'll be able to try before you buy — and maybe even score some apps that you previously deemed too costly.