Since my first batch of resin casts, I've been tweaking my technique a bit and experimenting.
The first thing I discovered is that somehow in my head I had the climate requirements of concrete and resin mixed up - while concrete sets best when cool and slightly damp, resin prefers a nice dry heat. Since the house is currently about 72 degrees Fahrenheit, this means that the resin casting session now begins with making a hot cup of tea while I hold the component bottles under my arms to warm them so they'll blend properly. This seems to be helping with the excessive bubble problem (though when it's overall bubbles rather than just a few air pockets, it looks kind of interesting).
The second thing I discovered is that the resin stays where you put it (this brand, at least). It neither shrinks nor expands while curing, so the molds should be filled where you actually want the resin to go. As you can see in the picture above of the first batch, I overfilled the mold a bit, and have some cleanup to do. Luckily, the resin is pretty easy to trim with an X-acto knife and a steady hand.
All in all, a lot of fun - I've been playing around a bit with embedding objects in the resin as well as making my own molds using liquid latex, and hopefully should have some good examples to show off in a few days. Finally, a use for all the little clockwork bits I hoard!