Nobody wants to admit they play out of tune. I certainly don't want to...
Most people just try to listen, and fit with what they hear.
That being said, intonation is pretty dicey issue, even with professionals. It's much less empirical than, say, tounge speed. Often times, opinion comes into play.
I've been using the Tuning CD for months now, and I can honestly say that when used in a consciencious fashion, it provides results. It's uses just intonation, instead of even temperment. This allows you to really get into tuning different keys--a tuner doesn't help in this regard.
For me, it shattered a lot of naivete concerning my pitch.
Considering the amount of money I've spent over the years on gadgets and mouthpieces, I'd say the Tuning CD is easily one of the best expenditures I've made.
James