What if your POP3 server goes offline? Also this happened to Hotmail recently and the problem was fixed. Could just be a little bit of instability in the cloud. If they have good back ups as well, they should be fine. Cloud computing is the way cause it's so much cheaper and much more flexible than dedicated set ups. Once the kinks are worked out, it will be a safe source. I also host my site on a cloud and ive been up 99.9% of the time over the last 5 months. I think I went down for about 2 hours tops.

But I mean, if your Pop3 server is down, you cant retrieve them in the first place...right? The problem with local storage is that you need to take your device everywhere. I used to be an MS Outlook kinda person but now I just use google apps to manage the site's emails.