I used to work on a project that interfaced with both SABRE and Amadeus and "just works" isn't how I would describe it. The thing is also quite slow and annoying, as it's interface is optimized for the trained operator to use it in a terminal setting and not for us poor shcmucks calling it through some weird API bolted on top.

Also, try to retrieve a PNR on an airline website or do like anything on the airline's own website -- the UX is usually pretty bad and the data loading takes forever. For that too the GDS is to blame.