Network proxies or so-called "WAN accelerators" have sometimes been deployed especially in the commercial world to speed up communications between remote sites. They may be applicable when tuning end hosts is difficult. However, these are often not designed for gigabit-grade networks in mind.
Some discussion also on nanog: http://www.gossamer-threads.com/lists/nanog/users/105809
-- PekkaSavola - 13 Jun 2008