I am with kei.isomura's definitions of 僕 and 俺 as well. Some additional input on the pronouns: 俺 is very casual, so you would only use this in front of good friends or peers. 僕 is the safe bet when it comes to a man referring to himself. 僕 can also be used in front of good friends, but it has a softer tone than 俺, so if you want to look "hardcore", you would refer to yourself as 俺. However, when you are at a workplace or in a formal setting, then it is best to use 私（わたし or わたくし）, whether you are a man or a woman. Using 僕 during a meeting may make you sound a little childish, depending on the atmosphere.

僕 can use any young adult even boyish girls. I think this pronoun is not use in official events. Other hand 俺 is used friends talk. Also Elder young men use this pronoun when they talk with younger person. I believe there is no limitation in usage but those are preferable not use by non-native Japanese speakers.