Despite what Google may tell you, Google Apps is not ready for companies that currently depend on Microsoft products. Companies without formal processes to enforce change usually have many employees that prefer to work within the familiar confines of Outlook -- and why shouldn't they? it has served them well for many years. If you are thinking of moving to Google Apps, please read this first.
These real-life observations are being made by myself -- the domain administrator for a company with close to 100 employees that have been using Google Apps for just over 6 months.
Let's start with Gmail. First, deliver messages via POP that are sent to oneself -- it is the first thing people do once their mail client set up. Domain administrators will hear several complaints about this with varying levels of urgency (sometimes by the same people over and over again). As a domain administrator, all you can do is tell the user "that's how it works", and "I will file a suggestion". Even if you are paying for the service, a telephone call will yield similar results -- none, or at least the perception of none.
Then you have users who "don't get some mail" -- this usually happens to only the most important messages. There are several probable causes for this -- messages are either labeled as spam (in their Gmail interface which many business users never log into), the message sits for hours in a queue somewhere (especially handy when an urgent message is expected to arrive instantly), or they genuinely didn't receive the message (which should never EVER happen). Domain administrators hear about every message that doesn't arrive -- and again, there is no way to offer a real solution or explanation to the user.
Ok, so some people might say: "Then why don't you just use the webmail client like you are supposed to?". That's usually what I recommend to users when they are having trouble, but they soon realize there is no offline access, signatures have to be in plain text and/or they get a message that looks like it's from a James Bond movie ("error code 007") with no explanation why or estimates for when it will be fixed.
This usually isn't more than an annoyance for personal use, but businesses users have a whole different set of expectations. How about meaningful error messages, features that business users want, and tech support that is a little more helpful than a forum with hundreds of people complaining. That would be a great start.
That is only part of the reason why most users only use the engine of this brand new car though. Outlook syncs email, calendar and contact information easily and effortlessly with the software available on most mobile device. On top of all that, users typically don't like change.
I could go on for paragraphs about complaints that I have received from my users, and even longer if I wanted to give real examples from people on Google's suggestion group -- but I will leave it at that. If you want to do some more research on your own, you can get a great sense of problems that plague users here.
That said, Google Apps does work for many people -- and some of you may have a corporate culture that is very forgiving and embraces change. These are ideal candidates for either the free or enterprise version of the product. But for the rest of you, I urge you to keep away from this product until the tone on their suggestion group switches from "this doesn't work!" to "it would be really cool if".