There's no need to create folders to organise your email. After you've read a message just click 'Archive' and it's removed from your inbox. Now in the future if you want to find any information about that specific email just type in the person's name, or their email address, or any words relating to the email, and Google's superior search technology will offer answers in seconds.
Don't forget when it comes to searching to use double quotes for an exact match. If you search for birthday cakes (with no quotes) you'll get results on both birthday and cakes, as well as birthday cakes. But search for 'birthday cakes' and the results will only list information relating directly to 'birthday cakes' and not Christmas cakes etc.
Labels
Use your own custom labels to intelligently organise your e-mails in any way that make sense to you.
For example, let's say your wife e-mails you something about your upcoming trip to Paris. Google mail allows you to easily attach labels to that e-mail such as wife and Paris. Later, when looking through your wife e-mails, you'll find that email message there, or when looking through your Paris emails the same message will be there. No more having to figure out what single folder each message needs to go into.
Conversations
Your email messages are organised as 'Conversations' so back and forth messages on the same subject are grouped together and organised in a logical way. As new messages on the same subject are sent and received they are added to the conversation.
Spam detection
Sadly there's no perfect way around the spam problem but Google's filters are some of the best.
3GB of online storage
You might think that you don't need so much storage space but why delete an email or file that might be of use in the future? Why not just archive it and you'll still have access to the information several years in the future.
Computers are as much about sorting heavy loads of information as anything else so it makes sense to archive and keep every email sent to you that may even slightly be of importance to you down the road. After all it doesn't cost you anything.
Mobile Access
Email when you're on the move is not for everyone but with the right mobile phone and internet access GoogleMail will work really well. Also, with Google's new mobile phone operating system Android about to explode on the scene over the next few years expect more and better email integration from mobile phones in general.
Access Anywhere
Computers are heading into the Cloud where all your data is stored at one central location. This means that all you need to get access is a computer to log into.
Impossible to lose your data
Have you ever had a hard drive failure when all your data is lost? If yes you know the problems and heartache this can cause. If you haven't then it's probably just a matter of time before you lose everything unless you take your backup procedures seriously.
But when your data is stored on external servers (in the cloud) it's impossible for you to lose any of it.
For more information this link has a good overall summary of the benefits of GoogleMail.