Apologies for an off-topic message, but I think this is important. Read on.

Yahoogroups just did something outrageous: they silently added something
called "Marketing Preferences" to your user profile, and the default is
opt-in for spam. Yes, that's right. Check it out for yourself, below.

I recommend you set every item to "No" as soon as possible, but that's not
sufficient as far as I'm concerned.

Yahoogroups has been pursuing an increasingly aggressive and unethical
business stance, progressively rendering their services worse than
useless. Try accessing the mailing list archives to see what I'm meaning.
Popups and forced ad display are getting more and more frequent.

Basically, they defaulted on their informal contract with the user (the
original terms of use with egroups.com and onelist.com), and as a result
I'm moving all my lists to a private host (which at $9.99/month is a much
better bargain than Yahoogroups no-ad option). I recommend you vote with
your feet, and do the same.

(Notice that there's no such thing as a free lunch, so you'll have to pay
for anything advertised as free in the end, even if the resource is
donated by volunteers. This is the reason I went with a commercial host
right from the start).

Have a look at your "Marketing Preferences" at:

http://subscribe.yahoo.com/showaccount

The default is set to "Enroll Me" to

New Yahoo! features and events.
Exclusive offers, online sales, and shopping tips on Yahoo!.
Travel specials and exclusive deals.
Managing personal finances.
Entertainment, games, and sports.
Finding a job or an employee.
Meeting someone special or a new friend.
Staying in touch with friends and participating in online
communities.
Managing my time and contacts.
Using Yahoo! for research and surfing the Web.
Building web sites for personal or professional use.
Ways to sell things on Yahoo!.
Tools for growing and managing a business.
Special offers from selected Yahoo! partners brought to
Yahoo! Delivers.

Edit Email Addresses
Indicate the email account
where we should send the
special offers and marketing
communications you have
selected, and your Yahoo!
Newsletter.

Other Delivery
Indicate other ways you want to receive the special
offers and marketing communications
you have selected.

http://help.yahoo.com/help/us/privacy/privacy-23.html

What are marketing preferences and did Yahoo!
change my preferences?
Yahoo! has grown and changed a great deal over the
past few years. In order to keep you up to date about
our many new products and services and how they
might be of use to you, we have created a new
Marketing Preferences page within the Account
Information area. It is designed to make it easier for
you to manage the marketing communications you
receive from Yahoo! and ensure you get the latest
relevant information to meet your needs.

In addition, we have reset marketing preferences for
some of our users. If you are one of those users,
unless you decide to change these preferences, you
may begin receiving marketing messages from
Yahoo! about ways to enhance your Yahoo!
experience, including special offers and new features.

Yahoo! is notifying users of these changes to
marketing preferences via email. Your new
marketing preferences will not take effect until 60
days after the date the email is sent to you so you
have plenty of time to decide what you want to
receive and what you don't. To change your
preferences, go to the Marketing Preferences page.

Please note that these new preference categories only
relate to how Yahoo! communicates with you about
Yahoo! products and services. Your Yahoo! Delivers
preference, regarding special offers from our selected
partners, remains as you selected it.