Many, if not most, companies are either moving services to the cloud, or at the very least discussing this internally. Moving your email to the cloud might have many benefits. The most significant benefit is probably cutting costs by not having to allocate resources on maintaining these servers.
If you are a Microsoft-shop and are currently running an on-site deployment of Microsoft Exchange, you might be tempted to switching to Microsoft’s (fairly) new BPOS service. The pricing for BPOS is a bit higher than Google Apps, with a price-tag at $10/user/month (compared to Google Apps Premium at $50/year), but if you want to stay with Exchange you might consider this cheap.