Much has been said about the automated build platform currently distributed with the Makerbot Thing-o-matic. I like it, but frankly, it doesn't work out of the box nearly as well as the rest of the bot. My acrylic ABP v2 sides both cracked within minutes of installation, so I've been searching for a solution ever since.
This is DEFINITELY a work in progress, but I'm currently using two of them as ToM parts :) I basically use it as an elevated HBP while I work on fixing the damn thing to be a proper ABP.
Print one each of the "b33bp uncut" and "b33bp uncut reflected" parts (a total of two plates on a well-calibrated machine with good skeinforge settings... takes about 4 hours for me). These new versions provide a cavity for a slidable m3 nut to adjust the ABP side fit to any imprecise X-cut in the x-stage. The new mounting holes allow for a Y-direction tolerance fit. You might want to dremel/sand down the Y-facing surfaces of the front and back plates before affixing them to the middle brace piece (providing more lateral tolerance in the Y-direction).
To be honest, I was basically able to shove mine in with very little modification/cleaning... but I'm working on designing a better fit for other circumstances. I use 18-20mm M3's on the top surface instead of 16mm's to allow for more lenient leveling.
I'm currently very inspired by the ToM tensioner things: http://www.thingiverse.com/tag:tensioner
Tensioning the ABP belt is definitely my next step. I want to go to bed/work and come back to several well made parts. That's the ToM dream, as far as I'm concerned.