this is a well-meaning but badly misguided stance to take. open source is a gift economy, and as one of the "producers" i am more than happy for people to accept the gifts i'm freely putting out there. the reward is getting to feel that i have made their lives better (and that too at no incremental cost to myself). in my role as a consumer, i likewise know that there are people out there happy that they have made my life better. there is absolutely no need to make people feel bad about taking from open source if they don't have the time or inclination to give anything back - that just cheapens the idea of a gift.
now would i like people to contribute by way of code, money or bug reports? definitely. but they should do so because that is a gift they wish to give to the ecosystem-at-large, not out of some sense of reciprocal obligations.
There's really no implied reciprocity to open source, though. Humans like giving gifts. It makes the work more enjoyable.
1) Beta test.
For example, the Firefox and Chrome nightlies:
http://nightly.mozilla.org/
http://tools.google.com/dlpage/chromesxs
A couple million hackers can help "upgrade" the Internet every day.
2) Ask/answer questions. You're making it a lot easier for the next guy.
How can I do X in Linux?
http://superuser.com/
http://askubuntu.com/
How can I do Y in Gimp?
How can I do Z in Inkscape?
http://graphicdesign.stackexchange.com/