Do you know LightSquared?

LightSquared (LSQ) is a company that is building a next generation broadband network, those of the "4G LTE" type.  This is a good thing because it allows us all to have faster, more widespread communications, staying online longer.  These networks work by transmitting signals from cell towers.  The issue with LightSquared is that they are planning on transmitting on a frequency that is right next to GPS frequencies.
 There's more to the story than that though.  First, you need to know that GPS signals, for better or worse, are extremely low power.  In fact, they are below the level of pure noise (~ -150 dB for you engineers). Meaning, if you were to listen for a GPS signal, on it's frequency (1575.42 MHz for L1), the static you'd hear would over power the GPS signal.  There are ways to track GPS of course, but that's another topic.
Back to LightSquared.  The original frequencies planned for use by LSQ were in the range 1525 - 1559 MHz, right next to GPS.  The broadcasting power has to be significant as well, to provide coverage to the cellular users.  Here's the crux: with their high power and proximity to the GPS band, most GPS receivers would no longer work.  The LightSquared transmissions would overpower the small GPS signals.  Here's a quote describing the problem:

One engineer involved in the debate (he takes the GPS side) provided us with an analogy:

What the FCC did was say, "While this was supposed to be a suburban neighborhood, we are changing the rules after 40 years. Company X has bought all the houses to the left of your house, and we are changing the zoning from your lot line left." As they bulldoze the houses (LSQ pays off Inmarsat to scoot over), you find out that they are going to allow them to build a concert stadium next to your two-post fence to the end of the block (put in GROUND stations broadcasting 3 billion times more powerfully than originally intended).

What happens? There's now going to be a U2 concert an inch past your lot line 24/7. There will be people fighting in the parking lot and the sirens of cops and ambulances going on all day and night forever.

Now—are they in your yard? Not at all. They are on their side of the lot line.

GPS is used by the military, civilians and in countless technologies worldwide.  GPS provides timing for bank and stock transactions (because GPS keeps time to the nanosecond level - a billionth of a second).  GPS will also be crucial to the next generation air traffic control system: NextGen.  If GPS signals are interfered with, these things don't work.
Since then, LSQ has proposed a new frequency plan that will alleviate some of the interference, but not all, especially for high-accuracy GPS users (surveyors, etc.).
Stay-tuned for more and keep a close eye on your spectrum, it's valuable!