With the recent updates, you can't really outline a % for keyword density. It all depends on the keyword and the niche. Some keywords naturally appear more on the pages ranking #1. One example would be "phone" - the first page ranking is Wikipedia with a description - "A mobile phone (also known as a cellular phone, cell phone and a hand phone) is a device that can make and receive telephone calls over a radio link while" - any SEO guy would tell you to decrease the number of times it's mentioned, but it ranks.
NATURAL!!!
Write articles that cover a subject, not just around the keyword, once every 100 words. Sometimes it will be even higher than 2%, other times it might be mentioned only once, both scenarios can rank depending on the other factors.