Hi there,
I'm working on an OpenFrameworks-based viewer for the output of gabebear's super-fast oscilloscope firmware, for the non-Mac people. I'm developing on Ubuntu but OpenFrameworks code should compile on Windows (and Mac too).
The normal OpenFrameworks serial library can't seem to handle "non-standard" serial speeds (like 2Mbaud) and it doesn't let you control the DTR line for resetting the Arduino (which this firmware makes heavy use of). I've got around this on Ubuntu with a wrapper script which sets up the 2Mbaud serial speed as a "custom speed" (using "setserial spd_cust divisor 12") and makes the DTR line respond to opening and closing the serial port (using "stty hup"). I'm not sure how to do the same tricks on Windows however, any Windows serial gurus out there?
So far I've been focussing on getting the code able to read the 10bits@124khz mode of gabebear's firmware (it can go up to 3.5bit@360khz, but I haven't written code to handle the different data-format that uses). At first I had a lot of trouble consuming the data fast enough on the PC side (using an EeePC), but now with separate threads for reading and display, I get a very stable signal. By the way, this speed issue is the reason I didn't just hack on one of the Processing-based Arduino Oscilloscope projects.
At some point I think it would be worth adding some more features to gabebear's firmware, like optionally reading two channels of input (at a reduced speed).
It's still pretty raw, so I haven't made the code public, but I thought I would mention I have been working on it in case anyone was interested. I plan to put the code online somewhere when it is more usable, but PM me if you are brave enough for unusable software 
pix.