I get the feeling that there are two alternate universes of hiring.
One is HR driven, heavily dependent on a hiring "process" that involves lists of skills with a little score placed next to each one for each candidate. These sorts of companies often use recruiters. An example would be a large bank that wants to start using SOAP for web services in Java, so they create a bingo buzzcard with (SOAP, JAX-WS, J2EE, and so forth...), call up the recruiter, and start matching candidates with requirements.
The other is very immediate and programmer driven. In this world, I have a feeling that open source contributions carry a lot of weight - not just because it's impressive, but because it increases the chance that the people hiring you have heard of you, used and read your code, and perhaps even worked with you personally. A prime example is 37Signals - which mentioned in a blog post that they probably wouldn't hire anyone they haven't worked with on open source in some regard.
The thing to keep in mind is that it takes just as much skill to hire in this context as it does to get hired. Very few organizations are talented enough to be contributing substantially to relevant OS projects. Of course, those are probably the ones you want to work for!
One is HR driven, heavily dependent on a hiring "process" that involves lists of skills with a little score placed next to each one for each candidate. These sorts of companies often use recruiters. An example would be a large bank that wants to start using SOAP for web services in Java, so they create a bingo buzzcard with (SOAP, JAX-WS, J2EE, and so forth...), call up the recruiter, and start matching candidates with requirements.
The other is very immediate and programmer driven. In this world, I have a feeling that open source contributions carry a lot of weight - not just because it's impressive, but because it increases the chance that the people hiring you have heard of you, used and read your code, and perhaps even worked with you personally. A prime example is 37Signals - which mentioned in a blog post that they probably wouldn't hire anyone they haven't worked with on open source in some regard.
The thing to keep in mind is that it takes just as much skill to hire in this context as it does to get hired. Very few organizations are talented enough to be contributing substantially to relevant OS projects. Of course, those are probably the ones you want to work for!