Here's the deal: I've got about 12 email accounts I use on a regular basis. I have one at bigmailbox.com, one at mail.com, a couple of hotmails, one yahoo and a few others. They're all pretty much exactly the same.
Gmail's been pretty different though, so much so that it's hard to use at first. For instance, all related emails in a conversation are shown on the same page, as if you're talking in an IM program. So, if I were to email Totem asking if I could worship the Alabama Black Snake and he were to email me back saying yes, it would appear on the page just like if we were talking via AIM or ICQ or something. If I were to then forward the email to Joph or Skeet, any emails between us relating to Totem's Alabama Black Snake would also be included in the message tree. You can click on the name of the sender to collapse that email down, to make it easier to view. But it's pretty fu[/b]cking handy to be able to track all related emails as conversations.
Another nice change is the massive data transfer and storage space they give you. You can attach files up to 10mb in size, and you get a full gig of storage. Nobody else is even offering CLOSE to that right now, and I'm sure that alone has yahoo and hotmail quaking in thier stylish-yet-affordable boots. And with 10mb of attachments, I can send my friend a couple of MP3s via email, instead of having to deal with the nuisance of FTP servers and the like.
There's also a pretty good spam filter. Early on it doesn't filter much of anything, but as you mark messages as spam it begins to learn what you consider spam and what you don't. I've been using Gmail for about 2 weeks now and I'd say 90% of all spam is stopped by the filter now. I haven't had it mislabel a valid email as spam yet, either.
There's also a built-in Google toolbar that allows you to search your entire email account for keywords contained in messages. So, I could search for "Skeet" and it would bring up every email in my inbox with that word, as well as all conversations related to those emails (in that nested tree format).
You can also mark important messages with a star, and then anytime one of the people participating in that email 'thread' sends you a message, it will be extra-visible in your inbox. You can also create 'labels' to mark messages with, and then in the future any time you receive a message containing that word(s) they will be dropped into a directory under that label. So, if I were to create a label for... oh, let's use the word co[/b]ck... Every incoming message containing that word would be automatically shown when I click on the label I created.
This is pretty nice if you participate in email message groups. I've got one for PS2 gaming that I belong to, so I could create a label for "PS2" and every email coming from anyone in that group would not only appear in my inbox but would also show up under the PS2 label.
Furthermore, you can archive old messages, and they will be data-compressed and stored for later viewing. So, realistically it's gonna be incredibly hard to actually use up that 1gb of storage they give you if you archive all your old messages.
THEN there's the Gmail Notifier, a little program that sits in your tray and will check your email at regular intervals, notifying you if you have new messages. Or, you could use your favourite Outlook clone since they offer free POP mail (so you don't even have to go to their website and view their very unobtrusive ads if you don't want to).
On the whole, the single problem I have with Gmail is the way the invite system works (though it's fu[/b]cking brilliant if you think about it). After you've used Gmail for a while, a little link on your inbox page will appear offering you the chance to invite a few friends to join Gmail. After you use up your invites, they recharge over time. This means that it's actually rather difficult to get a Gmail account if you don't know anyone with access, but it's a brilliant marketing strategy. The harder something is to get, the more valuable it is. People actively seek out Gmail invites just because it's not open for anyone to sign up whenever they want to.
I'll tell you one thing: Unless they make a lot of changes to the system in the near future, I am NOT going to use any other email service ever again. Gmail seriously is that good.