I posted two upgrades I've made to my MakerBot to Thingiverse this weekend. First is a build platform upgrade, which is just a quick mod that allows you to use "throwie" magnets to couple the build surface to the y-axis instead of the 1/8" cube magnets that come with the kit. While I like the original design, the larger magnets are easier to come by and you don't have to worry about them working their way out of the wood platforms over time because they're not held in place by friction.
Second is the drop in Paxtruder. My MakerBot has been down for about 2 weeks now because I cracked my idler wheel. I decided to take this opportunity to play around with an alternative design someone posted to Thingiverse that uses a Delrin pusher rather than an idler wheel. I modified the design a bit so I could reuse the mounts and heater components without too much difficulty. I haven't been using it for too long, but I love that it takes next to no time to change filament with this design and that tension is ridiculously easy to adjust. During the short time I've been using the new extruder, I've also noticed that the gear motor noise (and presumably load) seems more consistent as well compared to the idler wheel design.