Do F/OSS Contributions Make You More Marketable?

Bucking for a Raise asks: "Assuming that Free/Open Source contributions qualify as 'experience' in a professional sense, it would seem to follow that contributing would make one more marketable as an employee or contractor. Personally, I feel that I've gained invaluable experience from my contributions. However, I'm curious to know what other Slashdot readers have experienced: do potential employers/clients feel that it increases your worth? Does it depend on the visibility or perceived value of the project to which you contribute? Do the employers/clients you've seen place any value in, or even know about, F/OSS?"