What are mastercoins used for in Mastercoin? What are mastercoins used for in the Mastercoin system?

In Bitcoin, bitcoins are the only store of value and are spent as fees that the miners earn. In Ripple, ripples are used as a meta-currency accepted by everyone and are spent as fees that decrease the supply of ripples.

Does Mastercoin use any of those models? Are mastercoins the primary store of value in the Mastercoin system, or can one use bitcoins? Are they used for paying fees? If so, is anyone earning the fees and how?
From our FAQ


  The initial value for mastercoins came out of the fundraiser
  "anchoring". People were willing to "sacrifice" 1 BTC in exchange for
  about 100 MSC, so it anchored the initial value of MSC in at least
  0.01 BTC per MSC.
  
  The more general answer is that Mastercoin provides a set of features
  that only work with MSC or Mastercoin-based currencies, and there is a
  limited number of them. So, in order to enjoy these features, you have
  to own some mastercoins, giving them an independent value. The more
  real world usage Mastercoin sees, the higher the value of each
  mastercoin. In addition, as always, a lot of its value is currently
  driven by speculators executing a price discovery process.
  
  Specifically, mastercoin tokens are used for:
  
  Creating derived currencies and smart property are used to create
  and/or promote smart property tokens as an anti-spam measure.
  Mastercoins are used as the liquidity layer for Contracts for
  Difference The distributed exchange between Mastercoins and user
  generated currencies is more efficient than BTC&lt;->MSC or BTC&lt;->Derived
  exchanges - the latter require a 2 step commit process. As the
  protocol evolves, more direct usages for Mastercoins may be created.


I added this last bit about token usages to the FAQ following your questions - thanks ThePiachu for this questions!