This guide has the potential to be a great resource - the knowledge of tens of thousands (one days even hundreds of thousands or millions) of people brought together in one place - written by exactly the people that might want to use it.
I'm sure everyone who's used this guide has searched for something and been disappointed, and, whilst this is always going to happen for some topics (There aren't many experts on Stamp Collecting as a Political Influence in Post-Renaissance Botswana) sometimes you've been searching for something so simple, that there's bound to be someone who uses the guide who's knows everything there is to know about the subject, but just hasn't thought to write the entry yet.
Nobody knows - not even the fabulous powers-that-be - what people are going to want information on, so as much as those that bring you h2g2 want to provide entries on exactly the subject you're looking for, they aren't always going to know just what that is.
Whilst 'Ask H2G2' is there to answer any specific questions you have, if you want more general information on a subject that you're interested in, then you'll want to read a guide entry on the subject. If that guide entry isn't available then don't just mope, come here and commission one. I can guarentee that someone does know what the point of Lentils is, and it's an absolute travesty that the rest of us aren't able to share in their wisdom. The problem, however, is unlikely to be that they're keeping it a secret, but simply that they aren't aware that the rest of the world is crying out for them to impart their knowledge to us. So make yourself heard, and see if you can help out with any of the other subjects that people have requested.
So take a look at some suggestions for vitally important items that create holes that absolutely must be plugged, and if you have any suggestions for others (which I'm sure you will) discuss them in the forum, and I'll be sure to add them pretty soon.
And if one of the items is in fact the subject of your particular expertise then stop reading silly pages like this and GET WRITING.