Summary:  Who is mining Namecoins?

Those who don't care about exchange prices:

• People who want the coins for short-term use, to pay for registering and updating names, and/or purchasing products/services.
• People who want to support the Namecoin project for the long-term
• People who just heard about Namecoin and are testing it out

Those who care about exchange prices:

• People who seek short-term profit.  When they calculate the time is "right", they mine NMC in order to trade it into BTC, and then into a fiat currency.
• People who seek a long term investment.  They mine NMC and hold for the long-term.