Interesting, I hear people spelling out constants all the time when using the O notation to put emphasis where they want. I guess that's not really as universal as I thought, but I still think it's a good way to express.
It can cause more confusion though, if say you write O(kn), but the oh-notation hides a factor k^3, then it would be better to just write O(n). Or write O_k(n) to signify a hidden dependency on k. Or best of all, just write out k^4 n without any ohs at all.
