I use Google mail (gmail) as my primary mail client, as well as for my personal emails. While I see many advantages to using gmail, its certainly not a slam dunk as a choice.

The Good: Its free (but most other email clients are too), It accessible from anywhere with an internet connection (like on vacation — is that good ??) Since your email is not stored locally on your PC, if your PC fails you still have your email. There is over 6 gigabytes  of email storage which is a lot. It integrates with Google maps so you can get a map to an address directly from an email. There are various clients for smart phones/PDA’s that allow you to check your  email separately from your main email and access your gmail address book (for email addresses only)-I use the Blackberry version. You can pull up to 5 other email accounts into your gmail client so you can consolidate your email

The Bad: Since it’s online, you need an internet connection to read your saved emails.  You don’t have the ability to create folders and sub-folders (It uses labels to organize, but its only one level).  Reading through emails tends to be a bit slower than with a PC based email client.

The Ugly:  Google reads all of your emails and generates all advertising based on  their content. Since the free service is free, Google can change the terms of service at will. Google will update the web client from time to time and you will need to get used to a new client.

Full Disclosure: I receive advertising revenue from Google, Inc, but I am not being paid or encouraged to promote this product.

Google is a trademark of Google, Inc. Blackberry is a trademark of Research In Motion, Inc.