I've noticed this done on jcink, but would love the ability to have custom fields appear in the member list, i.e age, occupation, etc. I do run IPB3 not 4, but would willingly pay for a mod that would do this!

Hmm, not sure if I understand you correctly but I also run 3.4 and my custom fields also show on the member list, under "More Search Options". Or do you mean you want them visible at first sight?

Visible at first sight. here's an example of what I've seen on a jcink board: http://xxxx.jcink.net/index.php?act=Pages&pid=1

I have a plugin for that in 4.2, but I don't have 3, sorry  

It's ok @ChrisVanMeer

Hopefully I'll find someone who can help me out, or work out a way to do it myself, although I'm not terribly code savvy!