Still haven't jumped into the Gmail bandwagon? Maybe you need more reasons to figure out why it works well over Yahoo! Mail or Windows Live Hotmail. Here are some of them (in no particular order of importance):
 

1 Anti-spam feature is just amazing

I've been using Gmail as primary email client, while not entirely abandoning my Hotmail and Yahoo! accounts. When it comes to spam protection, Gmail does it best; I hardly see a spam message in my inbox. Yahoo! tells me by clicking a spam message it didn't detect, I am helping SpamGuard perform better.

2 Firefox extensions

If you use Firefox browser, Gmail allows you to take advantage of its productivity features. Change your Gmail skins, use spare Gmail storage for files and photos, manage tasks, manage multiple Gmail accounts and more.

3 Less distractions

Hotmail displays lots of colorful ads that distract me while reading or typing emails. Worse, Yahoo! forces me to view the ads by disguising as "introducing a new feature of chatting with friends". After login, both Hotmail and Yahoo! Mail display intermediate pages which contain boatloads of ads, news feeds even if it's obvious that the reason I logged in is I want to check my mail. Gmail is more straightforward, requires less clicks and gets the job done quickly. And its text ads don't steal my attention.

4 Schedule events via Google Calendar

A single new message can be treated as an invitation to a party or meeting that date and time set in the email can automatically be synchronized with your Google Calendar events. This allows message alerts to be sent to you (or your intended recipients) of such gathering is coming up soon.

5 Association with Google applications

When you read an attachment, Gmail associates the file with its apps, so you can still read the attachment even if you don't have a Microsoft Office in your machine. Same goes with PowerPoint and Excel. Hotmail and Yahoo! are too slow to address this issue.

6 Gmail Labs

Gmail Labs provides exciting features that might become a regular in all Gmail accounts. Before that happens, you can play around with such features. Some of the featured ones I like include "Don't forget Bob" which tells me suggested recipients, Undo sending, and a few Google gadgets.

7 Threaded discussions

I didn't know what I was missing until Gmail introduced threaded messages, a la bulletin boards. I was able to follow the whole conversation without scrolling down on message history that are otherwise truncated anyway. Every time I receive a message response to an earlier email, it's easy to recall the conversation, without the need to check previous emails.

8 Support for other email accounts

Gmail supports POP and SMTP connections so you can access all your mails in one Gmail interface. No need to switch browsers and make recurring logins just to check your messages. You can do them altogether using Gmail. Now that's productive.

9 Keyboard shortcuts

Mouse not working well? It's not a problem with Gmail's keyword shortcut support.

10 Filters

Gmail's filter function works well that you can reroute any message with "FWD:" in the subject into the Spambox, mark any email from a certain email address with a certain label, or forward any email message from certain domain name to a defined recipient list. 

11 Fast and accurate search function

Before Google Mail (Gmail), there is Google as a search engine. So we don't have to wonder how the folks have been able to deliver accurate search results (complete with keyword highlights for easy viewing). Comparisons revealed that Hotmail and Yahoo! paled in comparison.

12 No need to refresh browser to check for new messages

Gmail's clever integration with AJAX provides improved user experience. We don't have to refresh the page to retrieve new mail notifications nor reload the browser when we click "Reply" to a message. Other mail providers probably caught up with AJAX and also feature them, but not as good as how Gmail does it.

13 Large free storage

Gmail is generous enough to share gigabytes worth of free space so we don't have to remove old mails and retain sent messages with large attachments. Do you remember how much free space Hotmail allowed back then? A paltry 2MB! If not for Gmail's then-unheard-of 1GB storage, who knows if Hotmail would ever make an upgrade. Yahoo! offers unlimited email storage, but with the state at which it operates now, I hardly think that's an irresistible offer.