I have been using Ubuntu 10.04 for 2 years now and honestly, I am somewhat bored of Linux and wish to explore Unix (or Unix Like) now. I don't want a dumbed down version (like Ubuntu) anymore and want to experience Unix (or Linux if need be) in its true form. I basically want more to do with terminal and exploiting the open source nature of the OS.My requirements are plainlyNo dumbing down. I'll take a few shots in my knee if necessary.Awesome interface from parallel/high performance programming. I use Intel MKL on a daily basis. I use the computer ONLY for programming. So, all else (Flash support, Firefox blah blah) is useless.It should be extremely extremely stable. (Debian like)It should have good community support and long term support. I don't like changing OSes every 6 months.What would you suggest?(I have tried to make this question as objective as possible. Please don't give me a depends answer. Just throw a name if need be)NetBSD vs FreeBSD vs OpenBSD vs Other Unix/UnixLike vs Linux(I would really want to try a BSD/Unix now but then, if my requirements aren't met, I don't mind a Linux)P.S:I am not a N00B. I have tried Ubuntu, Debian, Fedora & RHEL but not long enough to make an informed choice. 
Help with OS choice for High Performance Computing
distribution choice
For exploration purposes I would say OpenBSD to discover how stable, secure and simple it can be. The basics of Linux will be Slackware.But this is in contradiction to your programming goals. So knowing about HP-Unix, AIX, Solaris, Linux Debian, RH and SuSE I would recommend using Linux CentOS 5.7 (or newer - keep it updated via yum-cron) to you.CentOS 5 is binary compatible to RHEL 5 and there are many tools around for the el5-branch (use rpmforge as additional repository - see the CentOS page about that).