I think a hybrid crochet-knit piece would work really well. And oh the possibilities available to you!!
I'm a much better crocheter than knitter, so I tend to "think in crochet" rather than "in knit." In particular, when a pattern calls for something like a small circle (such as for the eyes on an animal hat) or for straps on a dress, I immediately think of how to do this in crochet (and usually opt for that method). I, like the lady in pjs, have also created things where I knit the ribbing and then switch to crochet for the hat (or whatever). This works fabulously, by the way!!
Here are a few tips for combining the two crafts:
1) You really need to bind off your knitting LOOSELY (I usually bind off through the back loop). The key is to make sure you can get your crochet hook through the bound off stitches (ask me how I know!).
2) Keep in mind that crocheted fabric is thicker than knitted fabric when using equivalent needle/hook sizes. For this reason, you might want to go with a smaller crochet hook size and/or a lacy crochet pattern.
3) It's probably going to be a lot easier to pick up stitches on a crocheted edge that is straight. However, crocheting into an irregularly shaped knitted edge will probably not be a problem since you can usually choose where to place your "next stitch" in crochet.
Please do post a picture. I'd love to see your hybrids!