This info comes courtesy of a Travista newsletter that I get, so I thought here would be a good spot to copy and paste it:
In accordance with an agreement between the Russian Federation and the United States of America, effective September 9, 2012 US citizens can receive multiple-entry business, homestay/private, humanitarian and tourist visas valid for up to 3 years and allowing a stay of up to 6 months per visit.
Requests for this longer validity visa require additional documentation including a written letter of invitation composed by the host and a written letter of intent from the applicant specifying the visa validity requested.
In addition, the longer validity visas cannot be rushed; the processing time will take up to 15 business days. Applicants who need rush processing or who already have the official invitation from Russia, (hotel voucher and confirmation for tourists), can still use these documents to support visa applications. In this case the visas will be issued according to the dates on the official invitation as they have been in the past.
All in all, sounds pretty good to me