I often find the news here, so I'm very unlikely to submit something. And I only comment when I feel like I'm going to add value to the community or discussion, which isn't that frequently. So I have a clear judgement on when I contribute, it's not much or often, but it tends to present some value.
I've had an account for 2.5 years, and used the service for even longer, yet my karma is still less than 300.
I do frequently vote up good articles regarding programming, hacking, startups, and such things. That's the things I'm interested in since I was a young boy and that's my daily life. I'm a freelancing coder (yes, I see that term as positive, same way as hacking) since '96 and tried my own startups since then over and over. That said, I value good and constructive and sometimes also funny comments and being able to upvote them I frequently do so.
Are my upvotes even counted? I don't know, I don't really care. But I admit it gives a bit of a strange feeling to be "less worth" in a community where you participate - we can argue about that - daily.
Nevermind, just wanted to say.
Small addendum: After submitting this comment I remembered that I wanted to add that I'm from Europe and people not being from the States and therefore in a different timezone often experience to comment on already discussed topics (this also happens on Reddit a lot). Maybe this is also a part of why I'm not commenting that much.