Planetary's approach to microsatellites is VERY daring. Instead of flying bulletproof, radiation-hardened single vehicles (like NASA or JPL), they plan to put up scads of cheap, disposable spacecraft using off-the-shelf hardware.

This is an uncommon approach, and IMO it perfectly meshes with their exclusive use of unmanned vehicles. Who cares about reliability, it's just a robot and there are many more where it came from...

As an example of the "off-the-shelf hardware" thing, they are even looking at using WiFi (and high-gain antennas) to communicate with orbiting satellites until they can get laser communications (or enough money to buy time on the Deep Space Network).

EDIT: Another example is that instead of a purpose-built real-time OS (like VxWorks, which JPL used on the Spirit and Opportunity Mars rovers), they are using Linux with a real-time patch. Maybe it's not quite as reliable, but it's much more powerful.

Source: Planetary recently gave a talk at my university. I'm sure most of this is up on their website as well.