There’s been a very interesting dicussion in comments on Scott and Anton’s post about the strengths and weaknesses of MathOverflow and nLab, and I thought it might be good to divert to a new post (and use my position as blogger to top-post my thoughts). (edited since the original post. Look below for more)
Now just a moment ago, I followed a link, and started reading the n-Forum, and as a result, discovered that nLab has no page on knot invariants. And I thought, “hmmm, someone should fix that, and I guess that someone should be me.” So, I clicked a link, ended up with a blank page on knot invariants, and immediately realized that that person shouldn’t have been me at all.
What it comes down to for me, is that when I try to edit nLab, I always end up with a blank page, and no idea what I want to say. Andrew’s right that one should keep in mind that one is not writing Wikipedia (I think in my previous nLab forays, I lapsed into Wikipedian without even thinking about it). But still on some fundamental level, I had no idea what I wanted to tell people about knot invariants, or what they wanted to know. And “What knot invariants are.” is my standard explaining my research to a non-mathematician spiel; if there’s one thing I should be able to effortlessly write an nLab page for, that was it. And yet, it felt forced, and it was definitely not fun.
Whereas in my experience, MathOverflow is instantly absorbing and fun. Several other regular users have already told me they’ve found it an addictive time sink. I think the important difference is the level of feedback and interaction. On MO, one really feels as though other users are engaged with your questions and answers, whereas in nLab, I feel like I am talking into empty space. I think the other point is that the hardest part of mathematics is knowing which mathematics to do, so having a lot of concrete suggestions, not just for topics to write on, but questions to answer overcomes a real psychological barrier.
EDIT: Now that I think about it, there may be a good answer to this question. The sense I get from Andrew and Urs is that I haven’t been using nLab selfishly enough. I’ve been thinking about writing things that will be useful for other people, when perhaps I should be writing things that are useful for me to write, with some vague hope that other people will also find them useful and have input. Perhaps I will even try this at some point when I finish up a couple of current project and am in more of a reorganizing stage.
I think another point is that it would never occur to me to have an online lab book, because I don’t have a physical one. Some people (Scott M. and Aaron Lauda are examples that spring to mind) have physical lab books that they write lots of notes and calculations in. I don’t; I never take notes when reading papers, I write all calculations on random papers which I immediately proceed to lose (I’ve been using extra copies of a Number Theory exam recently), I never write anything down in any kind of structured form before I start drafting the paper. I’m not sure I know how to use a lab book, which is why I am probably not yet ready to use nLab.