alt Hacker NewsSlovenia joined EU rather fast (2003), so that might also have contributed to the prosperity. Joining EU is not exactly "breaking up", is more like "joining".
Currently, the rest of ex-Yugoslavia countries don't seem to do as well as Slovenia, and the main difference is date of joining the EU...
Slovenia has been doing way better than the rest of Yogoslavia for longer than it's been a country... it's one of the reasons they lead initial Days War. IIRC their GDP (regionally) was 6x the Yogoslavian average in 1990~