Nir's utilities and Mark Russinovich's PSTools are usually the first thing I download on a fresh Windows box.

I tried opening a 3M-line (550MB) CSV. It took a couple minutes to get to 1M, and it seems to have an O(n^2) algorithm because it was doing 40k lines/second on my machine and now (after around 1.5M rows) it's doing about 1/10th of that. Memory consumption is at over 2GB for this first half of the file.

It's definitely a nice tool, but it's far from instantaneous loading!