Everyone uses Gmail. I've been a loyal user since I got an account in 2004. Back then I probably got it just to show people that I've got one and feel important. To be honest, there was nothing new except perhaps the simple looking ajax interface and the conversations view. And yes, there was this big space available which they later started incrementing indefinitely. That was quite a change in email service that followed. It was only later that other competitors began expanding their users' inboxes. A few other things I liked about gmail was starred conversations, labels as opposed to folders, archiving and chat from within the browser. Remember meebo? Gmail labs came out mid-2008. Again, there was lot of excitement around the launch but I chose to ignore the new "cool" features. However, later I started using some of them.
Recently, I've started using gmail as my mail-client-in-the-cloud (Yay, cloud computing FTW!). That is, I use gmail at work (so I can take some time off and check emails from home). After the initial mapping of outlook folders to labels, I thought a lot more needs to be done to get the 'corporate' effect. Labs came to the rescue. Am going to list the ones I liked best and some more you might want.
Default 'Reply to all'; Google Calendar gadget - portable preview of your calendar; Google Docs gadget - access often used Docs; Multiple Inboxes - this one's amazing. I prefer this over their 'priority inbox', do try it; Navbar drag and drop - move around some of the gadgets above plus chat window; Nested Labels; Quote selected text - very useful when you're replying only parts of a long email; Send & Archive - reply to an email and hide the whole convo from your inbox; Sender Time Zone - doesn't seem to work sometimes. Supposed to show the time of sending in the sender's timezone (against the current time there too!); Title Tweaks - Gets the "Inbox (2)" before "Gmail" in the title so you can know from other windows; Undo Send;
I use most of them given above. Additionally, I use Inbox preview which is great while you wait for gmail to load. Especially if you clear out your inbox and organize them elsewhere. There are a few more like Superstars, Quick links which I might try but I haven't got around to try it. This is how my inbox looks like (you can't see all of what I've used, though):
I think Labs is a great idea. It makes sense to not confuse users with too many options and yet make them available optionally. I think users to should take time to try everything Labs has to offer and if possible contribute.
Outside of Labs, users with multiple emails, calendar and/or docs should try and integrate everything inside their gmail inbox. Personally, am excited by what Google has done so far and what they're to create in the coming days.
PS: I do wish they remove the "96 invites left" box from my gmail. Really, who needs it anymore?