You know you don't need to press Ctrl for sysrq combos right?
You might. For instance, under KDE or Gnome where hitting Alt-Printscreen/Sysrq might just cause a screenshot to be dumped. http://en.wikipedia.org/wiki/Magic_SysRq_key
If it's supported in your kernel. Fedora and Ubuntu kernels, by default, do not (part of why I run my own kernel).
I'm running Ubuntu Server (precise, 12.04.2 LTS) and SysRq is enabled by default.