10 is above average these days. I use this to keep an eye on the cookies
http://www.rexswain.com/httpview.html
It's useful to check these things when joining a new program, but ultimately we must judge the program on the rate that we earn money from it.
I reluctantly promoted a program with a 1 day cookie, it left me with the feeling I was getting scammed, but it did sell better than some programs which have 5 day cookies. If I see a 30 day+ cookie I normally jump straight onboard and enthusiastically send traffic over, then after 10,000 clicks I'll see if it's paying.
Though this is not an exact science, you can often get a idea of who you are dealing with by the length of their cookie. (Note: Some have it on default and don't even know they can change it)