I wrote in the main PD thread that I wasn't going to do this, so I thought I'd sneak it in over here. There seem to be two main "issues" with using the PD as far as I can tell so far. One is that the air coming out of the tube is hot, and some people find that adding a length of tubing is a good way to cool it down. It's also possible to cool things down a bit by taking in cool air along with the vapour. The other "issue" that can cause trouble with beginners is the speed of the draw. It seems easy to suck too hard and therefore not get a good vapour flow. I had some silicone tubing lying around, so I thought I'd try some experiments.
http://img91.imageshack.us/img91/4020/tubepa6.jpg
I found that the addition of this small amount of tubing was just enough to restrict the airflow and allow for greater control. It's still possible to draw too hard, but it requires more effort to do so. I also tried lengths up to about 10cm, which also seemed good, the longer the tube the more restricted and less direct it felt. It's worth experimenting to find the amount of restriction that suits the strength of your draw.
The restricted flow forces the air to move more slowly through the plant material ensuring good vapourisation. With this setup I felt that the vapour flow was more immediate and 'on tap', with small draws able to deliver good vapour, kind of like sipping a drink through a straw.