The real benefits of virtualisation are usually;
- not having to buy extra servers - in your circumstance you've already bought new servers so this point is moot.
- the ability to have zero-downtime hardware and base-OS updates through live-motion/vmotion - well this is great but requires shared storage - you may or may not have this in place.
- the ability for a VM to restart on another host in the event of sudden hardware failure - again relies on shared storage
- virtualisation usually impacts heavy disk use the most - in your case both Exchange and SQL server can be affected heavy by virtualisation more than many other applications if very busy - at least you know you're getting the full benefit of the hardware even if you missing out on the virtualisation benefits above.
There are some other minor benefits of virtualising (driver stability, shared memory, fault-tolerance mode etc.) but these are the main ones.
It depends on how busy you expect your Exchange and SQL boxes to be but you could have folded these four servers into one a single virtual server (you'd have needed more memory) or two servers if you's wanted the resilience features mentioned above (you'd have have to buy shared storage though).
Personally I'd have virtualised the DC/AD box and file/print onto two boxes for resilience, possibly the Exchange too if it wasn't being hammered. I'd have left the SQL box physical with the possibility of a backup cluster member running in a VM - but that's me. It's a shame you're asking this question now, virtualisation is pretty much the norm these days.