Why is it that hotmail.com and yahoo.com email addresses are viewed with a certain disdain by technical folks, but gmail.com has a different and higher status?
Is it that Google is (or was?) more respected than Yahoo or Microsoft?
I have actually seen services that specifically say that yahoo addresses are not allowed but gmail is ok. Gmail obviously isn't less anonymous, so it's not about pretending one address is somehow traceable and another isn't.
Is it a spam filter issue? Is the Yahoo spam filter so bad that folks' emails get lost in there, when they should have landed in the Inbox? Or does it have to do with other people spamming/spoofing from real or pretend Yahoo accounts? It's hard to imagine there is a server-based solution to that problem that gmail can implement but Yahoo Mail cannot, given the open standards for email and history of the spam problem.
There's also a fashion aspect. It seems perfectly respectable for a pro geek to use a gmail address for work, while a yahoo or hotmail (is that Windows Live now?) address somehow smells a little suspect. In particular, hotmail.com is below yahoo.com in respect, and other anonymous inbox services fall even further down.
There's definitely some groupthink at work here... if you have ideas as to what/why/whence it is, please comment!