Network World : Microsoft and Google fight over e-mail, but agree on $5 inboxes

"Price isn't the only consideration, of course. IT professionals in many cases are still wary of moving mission-critical applications such as e-mail outside their firewalls because of security concerns, and have complained about limited functionality in cloud-based tools." ~ Jon Brodkin

http://www.networkworld.com/news/2010/081610-cloud-email.html?page=2

I like how prices have come down in this area, but as an IT security guy I have to realize that once it is out of your control, it is out of your hands. If a hacker wants you email info while you have it in your network, they have to break into it. This also means that you will know that it happened, it may not be right away, but if you are a decent ITSEC guy you should find out fairly quickly.
We have to remember that by putting things out on the "WEB", they are mainly out of our control. It may be easier to get your items there, but the protection may not be up to your standards. At the point when you set things outside your network you deal with the other company's security policies. You need to make sure that they will meet your needs and standards.