GMail and Google Apps for Your Domain capacity is now 6 GB. That’s per user.
Using GMail and GA holds many benefits. If you configure it from your domain’s registrar console, your email will work even if your hosting provider is having troubles. It means less downtime for your emails.
Also, emails do not take up space on your server or hosting account. If a user does not download messages off the server, spam will quickly multiply. I’ve seen over a gig of spam in one user account before! Depending on your hosting package, you could be scratching your head wondering why you can’t upload your 200k picture to your website.
The GMail interface for webmail is second to none. Searching emails, organizing emails, sending/receiving, anything you want from a webmail client… GMail powers it better than any other free alternative I’ve used (and I’ve used most, if not all, of the major ones).