I want to report that I did my first printing from LR4 today and I am really delighted.
I have had an ongoing problem with LR2 and 3 of dark prints. The experts all say "monitor too bright," but my monitor is calibrated and turned all the way down to 90 cd/m^, which is substantially below the recommended 120 cd/m^. And it printed properly from other applications. I tried various remedies - a work-around in the driver, custom curves that I applied just before printing, brightening presets, including one from Matt Kloskowski, etc. - but nothing ever seemed right. I know from seeing complaints in various forums that I was not the only one. Well I'm glad to say that Adobe has responded to the problem in LR4 and the Print module now contains adjustment sliders for Brightness and Contrast. These adjustments are made in the application-to-printer data stream so you don't see any change in the preview which remains as you edited it. Consequently, you have to do some testing to find the proper level to get a print like the preview. I finally settled on +20. This together with the ease of fine tuning a soft proof virtual copy to the printer profile has made printing an absolute delight.