Change in main structure, now I'm planning on building my printer with 1/4" acrylic. It's waaaay cheaper than making it out of aluminum and will be lighter. It's also much easier to build an enclosure so I can heat it instead of just having a heated build platform. Airflow for working with PLA will be harder, I'll just have to build it into the design instead of propping a desk fan up pointed into my printer like I did with my makerbot.
Switching to t-slot construction makes designing and machining the parts far easier. Also I don't have to worry about the machine racking like I would have had to with the earlier design.
For comparison, here's the old and new designs. The shafts aren't structural, they're a part of the design I haven't put in the new version yet.
The new design is about the same size as the old one, but it's much easier to scale. It doesn't need nearly as many slots as it has. I put in so many since it's easier in Solidworks to pattern the slots like that than only putting a few in. As far as I know, the main difference will be it'll take a little longer to cut it out.