Also use a 21/4 from CV which slowly is becoming my favorite lens and the most used. (close to a 35mm at 32mm). I also have the 28/1.9 which is my night wide-angle (though 43mm is not really wide...) and have just bought a 15/4.5 on the Bay.
The 21/4 does vignette quite a bit, but as said above, it can be removed efficiently with Epson Raw or Lightroom. Most of the times, I leave it as I like the special look it give to my pictures.
Finally, the only concern about the 21/4 is lack of framelines which is annoying as it usually takes me more than one shot to get my subject composed correctly. I am therefore on the market for an Epson R 21mm finder. Good thing is that I can probably use my 21mm standard finder that came with the 21/4 on the coming 15mm due to the crop factor.