I just wanted to add that not all Yahoo email addresses are free accounts. I have two different Yahoo addresses that I use for different purposes. One I use almost exclusively for eBay. The other one and the one I use for most everything else is a PAID Yahoo account. I pay a fee every year for this account and it always irks me that there is no distinction.
The reason I never use an isp account is that I live in a small town and had to change the address every time there was a new provider which happened once too often. I like Yahoo because when I travel, it is easy to check my email no matter where I am.
So there are legimate reasons for using a Yahoo account. You cant always judge a book by the cover.