I just kegged an English dark mild and decided that I would keep it true to style by naturally carbonating. I used an online calculator but it just occurred to me that I had checked "bottle priming" rather than "kegging" because the latter only gave force carb settings. I primed with 2.3 oz. of cane sugar.
Kegs are supposed to have less priming sugar than bottles, right? I guess this calculator does not account for that -- http://hbd.org/cgi-bin/recipator/recipator/carbonation.html
You can bleed off a little pressure every now and then. Just pull the relief valve for a second to let some co2 out. If it is over carbonated you can bleed more off when it finishes. Its no biggie really.