I've done a lot of bobbin work on my art quilts. I use my PQ1500s which has the vertical bobbin rather than the drop in bobbin. I've used RazzleDazzle and other thick, lumpy threads that wouldn't go through a needle and it works very well. On the PQ1500s you just use your regular bobbin case and if necessary adjust the tension on the bobbin case, though I've never had to do that. The only thing that can be a little tricky is that you are working with the quilt face down, so you need to come up with some way of orienting yourself. I usually do FMQ when I'm doing bobbin work, but you can also use the regular stitches.
Since I don't use a frame, it's an easy process to switch back and forth from using threads that can go through the needle to doing bobbin work--just a matter of changing bobbins. I keep a quilt sandwich nearby for checking tension when I'm switching between FMQ bobbin work and FMQ with regular threads.
I bought a special bobbin case for the PC420PRW (drop in bobbin), but haven't tried bobbin work with it yet. According to the info that came with that some of the decorative stitches can be used for bobbin work as well
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