I have something called a "Thordon Elastomeric Bearing" in my stern tube (no cutless bearing like a fin keeler, because it's a full-keel boat). I have had no problems with this bearing and suspect that when I install both an Aqua-Drive universal-joint coupler and a packless shaft seal, I will essentially improve the system as far as I can go.
Here's a page with a load of product PDFs and engineering specs:
http://www.thordonbearings.com/brochures.html