I recommend it and see the industry going this route in the near future. For smaller businesses this means your busier exchange (150+ users) and SQL servers. VMware makes disaster recovery so easy and low cost. VMware starter edition costs $1500, but you gain so much. Yes there is a limit to 8 gigs of RAM but what back end exchange box needs that much RAM? Having an average system administrator be able to move from one server to another even with different hardware by just copying a few files and just power on the vm on the other server is a huge benefit in terms of speed and ease of use for administrators. Yes there will be some additional training on vmware, but with low cost bandwidth disaster recovery and business continuity can be a reality for all businesses large and small.
Converging technologies, lower cost of ownership for SAN technologies, carrier neutral data centers and pioneering companies like VMware, Vizioncore and Equallogic will help to accelerate this movement