I always take it for granted that people know certain things, like the fact that Google Mail is one of the most popular email systems available, and that it is absolutely free.
But I often forget that people have various interests, and I may have no clue of something that you take for granted that I should know!
Gmail or Google Mail allows anybody to create an email account, why not use it for your personal email, to keep the office communications clear jokes etc from friends. Have a look at Google’s 10 reasons to use GMAIL. The one point I find very effective is the fact that I can receive GMAIL on my cell phone, with a simple free application from Google.