I've been using a CarboNext petty for about 4 months now...and overall its a great little knife for the price. Nothing fancy, but gets the job done.
Stain resistance is really good actually. I'm definently less carefully with this guy then my carbon knives and haven't had any rust issues. As far as a patina goes...it really doesn't develop one like carbon. However, I did use it to segment an entire case of oranges (yay for restaurant week) the other day, and after that it did develop a nice dark gray patina...but that was from major exposure to acid, and it went back to its normal looking self after a couple of light washes.
Overall, I'm very happy with it. I bought it for a "nothing fancy, but still good" knife that I could abuse a little bit and not worry about it. And it has served that purpose very well...and then some. I'm planning on picking up a gyuto for home use
(woo, first post!)