I disagree with that Mouse.
A couple things that really stood out to me are automatic server queries, and threaded discussions. I would post a screenshot of some new stuff, but I really don't want to have to edit the screenshot, and there's stuff I would rather not share with everyone here.
E-Mail clients are well known for being much more fully featured than their webmail counterparts because of the robustness that you can put into a downloadable program. Some of the better mail clients have threaded discussions, which nest emails and their replies in a format similar to a message board. Google implements threaded discussions in a simple and elegant fashion. It's almost like having a stand alone mail app without the hassle.
Another thing I noticed was that gmail uses client scripting to query the mail server every so often to check if there's any new mail. I gave the source code for that a brief looking at, and I noticed that for Internet Explorer people, it uses the XMLHTTP ActiveXObject. I assumed from there that Mozilla users would use the XMLLHttpRequest object built in, and Opera users would likely use some other form of doing the same thing. (Perhaps a DOM Document).
Basically, what this means for the user is that you do NOT need to refresh your inbox to receive new mail. It will just appear in there when a new mail message is received. I can pretty much guarantee that this works on Mozilla/Mozilla forks and Internet Explorer. Opera/Konqueror/Safari users should probably give it a shot, but no promises.
As for the privacy thing, gmail is upfront with you when you sign up, and tell you all about how their system works. When you delete email, it may take a while for the email to be fully deleted from their systems, but it WILL be deleted eventually. The real difference between gmail and non-gmail is that you have no idea what microsoft or yahoo do with your email.
But regardless, I think it's a little bogus to be complaining about gmail's privacy. You agree to their terms when you sign up. They give you 1GB of space, and the fastest and bestest webmail interface I have ever seen. In return, they want to deliver ads to your inbox based on the scanned content of your email. As a consequence of the 1GB of space, it may take a while for emails to be deleted.
But personally, if their terms were to take a random sample of every 100 emails in your inbox, photocopy it a hundred times, send it around the office and laugh, I honestly don't care. I'm beyond the power of any insane US President or his merry men, as I am Canadian, and it's not like I am up to no good that often anyway. (And I use anonymous email accounts and spoofed IP addresses for such things anyways).
Short and sweet of it is that I love gmail. I think that it's just your standard knee jerk reaction that's generating such bad press.