"You couldn't pay me to use an existing desktop mail client over Gmail."
So, I understand having your email everywhere. That is a killer feature. But you can also provide that feature by simply having a web gateway to your IMAP mail.
What exactly is the killer feature of gmail? The tagging is nice, but other programs have similar features. Teh spam filtering is nice, but actually there are better spam filters. The only thing I can think of is the integration with google docs and I actually hate that feature. I don't know how they managed it, but opening a pdf with google docs is about 5x slower than downloading the pdf and opening with evince. So, it's pretty much a non-feature unless you can't be bothered installing a pdf reader.
I guess I find gmail useful, but I'd still rather use a normal email client if for no other reason than interruptions in my network connection don't affect working really.
As far as I know, the way Gmail handles conversations and archiving is unreplicated by any desktop client, and single-handedly the most powerful thing about Gmail. I now have a regular habit of archiving any message that doesn't have an actionable item, decluttering my inbox. If another message should arrive in a thread, I have the entire conversation history right there. A good desktop app could replicate it, but I could see this behavior being difficult to map on top of a standard IMAP server.
In addition, there are a ton of innovative small features (especially in Labs - Don't forget Bob!/Got the wrong Bob? have saved my ass multiple times with new clients) that I just don't see other e-mail clients implementing, and they're constantly rolling out new ones. The fact I can get the exact same functionality on any computer I happen to be on is just icing on the cake.
Ultimately: it feels like desktop clients have largely stagnated, while Gmail has an incredibly effective way of thinking about e-mail.
Have you looked at Outlook 2010. They have a similar conversation view. Outlook also gives you the ability to respond to mail with a phone call (Google must have this capability with Google Voice, but don't see it).
Another feature I like with Outlook 2010 is to see all correspondence from the person I'm currently looking at (email, meeting invites, chats, etc...).
There's also this cool thing called Quick Steps, where you can construct macros in Outlook. This is useful when you need to have specific workflow around email that you can put together in one click (like, when responding to legal, I need to send the reply, delete the original email, send another email to my manager, and send a note to OneNote).
And of course Outlook has a webclient, so I can access it from anywhere too. While Outlook is heavyweight, feature-wise, its pretty complete, and offers some other things that are hard to beat.
You couldn't pay me to use an existing desktop mail client over Gmail, either.
Other than reasons you already iterated, the killer feature for me, the one I truly cannot be without, is the threaded conversation view. I know some desktop clients have threaded views, but unlike Gmail's implementation, they suck.
While I prefer Mail.app aesthetically and for the purposes of OS integration, the thing it really can't beat Gmail in is speed. Search is incredibly fast (as one may expect), but also workflow: almost every action is a keyboard shortcut (or two) away. I'm not aware of any other web gateway that has these shortcuts enabled.
That web gateway has to be maintained and that is one of the biggest drawbacks over a hosted service like Gmail. If you don't constantly upgrade your server and your software one day you'll get rooted by some exploit bot.
Sure, if you have the time and patience to constantly maintain your servers, and you think your web gateway's UI is as good as Gmail (I don't) then go for it. I want to spend my time doing actual work though.
> but opening a pdf with google docs is about 5x slower than downloading the pdf and opening with evince
And yet I keep using their preview feature because it somehow feels faster than opening it in a native app. The actual stopwatch time doesn't matter, it's the perception.
I think this is the reason why people like Gmail so much: it feels fast, it feels comfortable to use. It's not so much the features; strip out a few features and I'd still use Gmail.
So, I understand having your email everywhere. That is a killer feature. But you can also provide that feature by simply having a web gateway to your IMAP mail.
What exactly is the killer feature of gmail? The tagging is nice, but other programs have similar features. Teh spam filtering is nice, but actually there are better spam filters. The only thing I can think of is the integration with google docs and I actually hate that feature. I don't know how they managed it, but opening a pdf with google docs is about 5x slower than downloading the pdf and opening with evince. So, it's pretty much a non-feature unless you can't be bothered installing a pdf reader.
I guess I find gmail useful, but I'd still rather use a normal email client if for no other reason than interruptions in my network connection don't affect working really.