When was MyBitcoin created?
The mybitcoin.com domain existed no earlier than 2010-04-25, according to the domain name registration record (whois).

According to the mybitcoin.com history at archive.org, the domain first appears to have useful content sometime in early February 2011.

In case the above archive.org url doesn't work (seems to have a problem for me), copy and paste it from here:

https://web.archive.org/web/20110315000000*/http://www.mybitcoin.com