We are one of the companies who it most definitely works for - we have about 50-60 enquiries a week and depending on the time of year a fair few are yell. When it has just come out we get about 50% of our enquiries through them. After a month or two this does drop but we still get a few.
I would advise trying it once - it may not be worth it but unfortunately with advertising you need to try it yourself.
A lot of people on here swear by community magazines - they never have generated enquiries for us, no idea why - maybe it's something to do with the ads we use that work in YP but not magazines?!?