Peter Biddlecombe's review of the CD ROM on Amazon shows that it's a favourite tool of Listener setters and solvers alike. Is it cheating? Is looking stuff up on the web cheating? If I could do a Listener without aids I would - I certainly get a kick from doing the Times without references, and on those occasions where I've only had the paper version of Chambers to work with, I've felt an extra sense of achievement completing a Listener. I get dead chuffed if I can do a Mephisto without aids (though I defy anyone to do this week's - more than half the entries go down in my book as "very obscure" and the wordplay doesn't help much). For me, Listener is not a race: time is less important than the journey, but the availability of a searchable dictionary mostly enhances the experience and cuts out some serious frustration. You've still got to work out what search terms to use, and if the grid entries aren't real words then you're back on the little grey cells.
I've also found that setters often don't give a straight Chambers connection, but one that is two or more steps removed: they're on to us, you know, and don't like to make it TOO easy!