As a fan and admitted abuser of Gmail accounts (I have one for each personality I guess), I have to pass along this CNN Money article about Gmail turning 10 yesterday. To summarize, CNN Money points to these particular Gmail features as the reasons why Gmail became the industry dominant e-mail provider:

• Size of space offered: ever-growing but initially 1 GB back in 2004, compared to Yahoo’s 100 MB)
• Google-search-enabled searching of archived emails
• Auto-save for unfinished email
• Undo send, allowing users 30 seconds to retract sent emails
• Priority sorting of important emails
• Integration into Google services