The last one I did was a complete f*** up. I don't intend to do any more 'freebies'. I think the numbers at the end of the night were something like £400 split between the two named charities, but over £2000 behind the bar. Organisers took the piss and it was pretty much a disaster from start to finish. We played well (as always) and treated the whole thing as a 'public rehearsal', but I'd come home early from a family holiday (by a couple of hours, but even so) to drive the hour to the gig and get home at 2am.
Not doing them anymore. If I believe in a specific cause or charity then I'll donate privately to support them, but to do that for a couple of hundred quid fora charity then really, I'd rather just bung them the money and stay at home.