The key bit of what they are trying to sell you is the 'push technology' piece. If you are already using a single client Outlook 2007 you are unlikely to see any difference at your PC end as you have nobody to share calanders with.
What the push technology does it make the mobile version of Windows mail look more like a Blackberry in that when emails are delivered to your mail box, they automatically get pushed out to your device, instead of what you do now which is dial in and do a 'send and recieve' to get your emails. On a desktop, all you will notice is that emails arrive a bit quicker because they are pushed to you rather than waiting for periodic check.
So - do you need your emails delivered to you immediately they arrive at the ISP or are you happy to collect them as and when you are ready.
If you are going to think about Exchange the cool piece you might want to ask them is about Outlook Web Access (OWA) If that is provided as part of the deal then it might be worth it. With OWA you can go to any web terminal, type in a URL and get what looks like Outlook with all your email and calander in it. Very useful if travelling or away from your home PC.