I've been considering recently whether I should use Gmail as my primary email application. I've used other web mail in the past, starting with Rocketmail that, I think, was taken over by Yahoo. I still have a Yahoo account, but only really use it for their Groups, especially Freecycle. I managed to get a Gmail invitation soon after it started via a site where people were passing on their spare invitations and was able to get my standard user name. The service was innovative when it started and has gained many features. I've not exploited all of them, but then I've been using it as a secondary account.
My main account is on this domain. I use Kontact to access it, but have used Thunderbird in the past. There is web access via SquirrelMail, but it's clunky compared to Gmail. I set up Gmail to access this account and it works quite well for that. I can make it use my mail address for outgoing email too, so my Gmail address is almost redundant. This is how I handle email when not at home. The down sides are that my outgoing emails are only on the originating system and there can be a delay before Gmail picks up new mail. There also might be issues with handling encrypted email on Gmail, whereas Kontact does GPG nicely. Not that I'm doing much encryption as few of my contacts use it.
Of course Gmail is not totally reliable. It was down for a couple of hours this week. That's not a big issue with my low volume of email and my own server has been down on occasion. Generally I would expect Google to maintain pretty high reliability. They can afford massive redundancy in hardware. They also do pretty good spam filtering.
When I got my new phone I was wondering how to synchronise my calendar and contacts with either my PC or Google. This was just as Google announced Activesync functionality. I've used that and it generally works. I had been using their calendar for a while so that I could see it from work.
So what reasons are there to not use Gmail and how do I make the most of it?