Personal example: I'm recently married, and you wouldn't believe the time my wife has had getting her username changed to reflect her new last name (an issue because her employer bases usernames/emails on their first + last names). This means she gets to explain every single time she gives out her email (internally) why its not the expected pattern, but rather a seemingly arbitrary string.
Its not the end of the world of course, or even that big of a deal when you consider it individually. But its one more thing that's not accessibly designed, and its hard to get a male dominated culture to care.
FWIW, I changed my last name too, but I own my company, and we use first names for our emails anyway, so I was lucky.
If you own your company, make sure you're getting this right. If you let people choose their usernames, and change them easily, you can cover this case and many others. [1]
[1] http://www.kalzumeus.com/2010/06/17/falsehoods-programmers-b...