"I wonder how I could, say, work on my Python (ipython with scipy and matplotlib) and Matlab (OK, Octave, but still) data analysis, while checking my mail, browsing the web and posting comments on El Reg."
If you're posting on El Reg you're not working on Python code. You're either doing one or the other. You may think you're doing both, but you're actually task switching, not multi-tasking.
And iPhones have been able to play 'DRM free music' in the background since day one.