This is a huge step for Google, and Android developers in general. Developers can now charge for their applications -- something that will surely make the ones with brilliant ideas, and the drive to turn them into reality, very rich.
Something that may cause some initial sluggishness in sales is the fact that apps have been completely free up until now. Having to pay for some apps may leave a sour taste in mouths, at lest in the short term.
Apple has been allowing developers to sell apps for a while now, and their App Store has so far been a huge success. Unlike Google, Apple has been encouraging developers to put a reasonable price tag on their apps, causing some developers to see 6 digit monthly revenues.
Another problem with Google's model right now is that they don't pocket any of the 30% they skim off the top -- instead, they give it to network operators to subsidize the extra network traffic that may result from these apps.
I have a feeling though, that once Google starts shipping Android for netbooks, that 30% is going to start finding its way directly into their own pockets -- it definitely has the potential to make them a ridiculous amount of money.