I like to think of a route server, when used for actual routing exchange rather than statistics collection alone, as a means of scaling eBGP by reducing the number of peers. That complements a route reflector, which is a means of scaling iBGP. Bay RS, at one point, made a distinction between a route reflector and a route reflector server, both for iBGP scalability. I'd have to do some digging to find out if the latter was more than a marketing distinction.
One difference is that Route Servers, like the ones run by Merit RSNG team, are based on the Internet Routing Registry, whereas route reflectors are not. Route Server routes are re-announced based upon configured IRR policy.
I also think of Route Reflectors as being both internal AS (IGP) and external AS (BGP) re-announcers whereas Route Servers are strictly inter-AS (BGP).
Bill
I've also heard some symantic confusion between route-servers and route reflectors. In conversation, I usually assume that distinction to be between functionally equivalent boxes operating in the plenum between a number of administrative domains (a route-server) or as glue between regions or ASes within one administrative domain (a route reflector). I don't know how common that understanding would be, though. Anyone have any better thoughts on the difference between a route-server and a route reflector?