Zeno-count me in as well please, but some kind of "ground rules", being eligibility criteria and record keeping quality is, in my mind, essential, so that we only help good causes.
I already do some "pro-bono" jobs and some heavily discounted jobs, but find it very hard to try to do the right thing by choosing the ones to help. I've tended to work on the basis of only helping "innocent" people - i.e. those who've really tried their best but have been beaten back by circumstances completely out of their control.
I've also found it difficult to decide who to take on, when many times there are other agencies offering the same support, i.e. Citizens' Advice, Taxaid, or even HMRC themselves if they manage to get through to someone who knows what they're doing.
Quite a number of times, I've been taken in by sob stories of people claiming they're broke, only to see relatively healthy amounts on money in their bank accounts, or investments, etc. Also quite common are people too lazy to sort out their paperwork or do any book-keeping - if they're not being charged for it, they tend not to want to spend their time sorting it out for you.
Despite the potential for "takers", I've always found the pro-bono work to be very worthwhile. I've seen the change in people from when they first come into see me, losing sleep and depressed, worried about the prospects of losing their homes etc due to ridiculous tax assessments and threatening HMRC letters, and then to see them happy again a few weeks later, all for the sake of a couple of hours work and a couple of letters to HMRC.
At the moment, my approach is initially to simply offer a freebie first meeting to try to get to the bottom of the problem. It's surprising how many times all that's needed is a clear head and an outsider's view, and they go away happily able to sort it out themselves once they know what's what and who they need to contact. I try to avoid taking over and doing too much myself.
It would be interesting to see the consensus view moving forward. I must admit, I really like the idea of a "UK business forums accountant" group offering this kind of help. Sometimes it feels like one big happy family of accountants on here - makes you want to help out eachother and work together for the common good. What a difference it is to some other fora (accounting web for one!)