I have been using Google Apps for my domain for some time now. I have also helped some of my clients get setup with Google Apps for their domain. Google offers many tools that are beneficial to the small business for a great price (many times free).
Before using Google Apps for my domain I had a GMail email address as my primary address. I used the GMail Notifier to let me know when I had a new email message.
Since upgrading to Google Apps, I have installed Google Talk. (UPDATE: Google Apps users, download here.) Google Talk has the GMail notifier built-in to the application. So with a single install I have a messenger client and the GMail notifier sitting in my system tray.
What's so great about this GMail Notifier? Well, with a simple glance to the system tray, I can know if I have new emails waiting or if all my emails have been read. If you take a couple of days to respond to Aunt Sarah's email she still may forgive you. But if an anxious client has sent you an email, you might want to know ASAP when you receive the email.
I am including two images: one showing email waiting and one showing a happy empty inbox.
As you can see, it's pretty easy to tell that the left image is showing I have email waiting to be read. The right image lets me know all my messages have been read.
The notifier is also constantly monitoring your inbox. Whenever a new message does come in, the notifier pops up a quick window showing the sender and subject of the message received. It is then your choice to pop over and answer the email or wait until you're at a stopping point in your current task.
This is a great time saver that keeps you from having to remember to go check your inbox. And maybe it'll be just the tool you need to keep those customers happy.