It appears as though democratic presidential hopeful Wesley Clark is a strong supporter of open-source software:

Here at Clark HQ, we're using a lot of open source technology. When our IT team was setting up computers for everyone, a good majority of them outfitted with OpenOffice and Mozilla. We're also using Thunderbird as our main mail client and Squirrelmail for the travel team. Those who refuse to give up their copies of Outlook are required to surrender their laptops for examination before being allowed to plug them into the office network.

Could we have a non-MS White House in the future? That would certainly be a very prominent endorsement of OSS.