I am in the gmail beta right now.
I can list some stuff for you all:
+ You probably already know this, but your replies are grouped together to form a conversation. It takes some getting used to but it's a neat feature. They also have something called labels to group parts of the conversation (so you don't have 20 different topics in one conversation)
+ You can search through your email, they also have filters where your email will be sorted according to.
Eg: anything that contains Gmail in the subject goes to gmail label under that persons conversation.
+ They have a spam section of your mailbox, however I don't see anywhere to enable or disable it, so I assume it's on and you can't turn it off.
+ Bits of the email conversation are shown before you even open the mail, kinda like google's searches.
+ It is noticably quicker than hotmail, yahoo in changing pages (maybe b/c it's in beta right now)
+ I read the privacy policy and the only thing I could see that violated any kind of privacy is them giving your name/ip info to the FBI if they are subpoena'd for it (but this comes standard with almost anything internet related) granted, I am no lawyer.
+ Some interesting stuff:
-My trash folder reads as follows:
--No conversations in the trash. Who needs to delete when you have 1000 MB of storage?!
-My spam folder reads as follows:
--Hooray, no spam here!
Go figure
If you have any other questions I'll try and answer them.