I've owned the 15" rMBP since June. I use it exclusively in scaled 1920X1200 mode. Fonts are pristinely rendered to my eye. I'm very skeptical that you're able to detect blur in the font outlines at any reasonable distance in properly optimized applications.

What program were you using when you noticed the blur?

I must've gotten one of the few MBP Retinas that looks great at the non-2X resolutions. The non-2X resolutions might not be as sharp as the 2X resolution, but its still very sharp, and leagues sharper than non-Retina displays.

In my experience they are slightly blurrier at the non-doubled resolutions, but still much, much better looking than on a non-retina MBP.

Were you looking at native cocoa text controls or at e.g. Chrome?

Text rendered by Safari in a web page.