I agree with you Avni, that kind of servers are really useful for the community. As Raul said, we (at UNED) have the official testing servers: running openACS (A) and dotLRN (D), each with PostgreSQL (P) and Oracle (O), so... 4 servers in total: A+P, A+O, D+P, D+O.
I will like to emphasize the difference between staging (or pre-production, or demo) and (automated) testing servers. I think both are important: testing for developers, and demo for final users or the marketing team.
I like a lot the way Viaro Networks show their work at oacs rocks!, and also ]po[ has a nice web, with a lot of documentation, a good marketing and a big online demo button.