I've been playing around with Cycles baking and running into a few limitations here and there. I've put together a pretty simple scene with an HDR image light, some reasonably simple bricks, a mortar mesh, and a bake target. I haven't tried the other passes, but both Combined and AO seem to have very high memory usage given what is being baked. Blender shoots up to 2.87 GB of memory usage on this fairly simple scene, while it uses about 133 MB (about the same as normal) when I just render. I did all my tests with the CPU only. If Dalai could run a debugger, try baking the scene for himself, and see if he can reproduce the rather preposterous memory usage, I would really appreciate it. I also tried baking with instanced meshes and it didn't seem to make a difference for memory usage.
To get all the relevant meshes into the scene for baking, just toggle layers 2 and 3 to reveal the source meshes.
Download the .blend here.
Using BF's official 2.71 build on Windows 7 64-bit. Processor is AMD FX-8320, GPU is a GTX 780 with 3 GB of VRAM. I have 8 GB of ordinary RAM.