Tired of Yahoo and want to try Gmail? Here's an easy guide to a hassle-free switch!

[edit] Steps

Export your contacts from Yahoo mail: Go to >> Address >> Import/Export >> Yahoo CSV.
Save the file on Desktop.
Log into Gmail.
Click on "Contacts" in the left hand sidebars.
Select "Import Contacts" from the options.
In "Browse," select the file on your Desktop. It will import all your contacts.

If you have important e-mails you want to keep, just send them to your new address.
You can use IzyMail to forward and import all of your current and future email to Gmail

[edit] Tips

If you want to abandon your Yahoo account, go to "Mail Options" in Yahoo. Select "Vacation Response." Write a short note to announce to correspondents to send all emails to your new Gmail address, which you specify. This email will be sent to whoever emails you on your Yahoo. So you may want to obfiscate your email ID: ie. ghost_post(AT)oman.om instead of ghost_post@oman.om If you want, you can also send a quick email from Gmail to your Contact Book addresses informing them of your change.
If you're willing to pay the $20 per year for Premium Yahoo mail and want to auto-forward your email from Yahoo to Gmail, go to "Mail Options" in Yahoo. Select "POP and forwarding." Choose "forwarding" from the list and enter your Gmail address. Press "send." (Yahoo! has recently discontinued some of its programs which charged for features. Reports vary, but some Yahoo! email users have reported this service now available for free. Try it on your account to see.)
It's possible to take your mail with you as well! Details are beyond the scope of this how-to, but check out http://mrpostman.sourceforge.net/ and http://sourceforge.net/projects/freepops/

Remember to check your Yahoo account occasionally in case you have received an important message which the sender has not forwarded to your Gmail. Also, Yahoo will deactivate any account that has not been logged into for four months, as it will be deemed a "dormant account" (http://help.yahoo.com/help/us/mail/access/access-04.html)
As of recent, Gmail supports both importing and exporting your contacts to CSV (comma separated values) file. Take note that Gmail's CSV file is compatible with MS Outlook (NOT Outlook Express), so if you want to transfer your contacts from/to your local e-mail client, make sure it supports MS Outlook CSV format. You can easily import/export address books between MS Outlook and MS Outlook Express though, but it's beyond the scope of this article.
Be cautious when using the "Vacation Response" as mentioned above. This will alert everyone who emails you what your new email is, no matter if you want them to know it or not. Some spammers do monitor emails that come back to them with software which can automatically add your new email address to their database.