1. While 3 GB in free Gmail is lot of space, it can get exhausted - Google Apps gives you 25+ GB of storage space.
2. You can define a list of approved email senders and web domains - any messages from approved lists will always go to your Inbox bypassing the junk email filters. You can also block individual email senders and entire domains - messages from anyone in a blocked domain go directly to the Junk Quarantine.
3. Google guarantees a 99.9% uptime for Gmail. If things still go wrong, you can call Google's 24x7 telephone support for a solution.
4. Google Apps Premier users can hide all advertisements in Gmail that show in the right sidebar.
5. Now the top reason for using Google Apps email over Gmail - accidents do happen but with Google Apps Premier, you can recover deleted email messages from Gmail.
If you accidentally delete an email message in GMail , you will be able to retrieve the deleted message for the next 90 days by just searching for the message in the email archive.
Unlike Gmail which is free, Google Apps Premier will cost you $50 per year. Though Google is promoting the premier edition for business users, it is a good enough for anyone who finds Gmail storage limited or wants more control - $50 could be a worthwhile investment.