@Mark: You can't - MSIs have a single flag indicating whether they should elevate or not. That's why I moved the 3.5 installer to a new format. Unfortunately, since we're in a transitional state, admin privileges are necessary to install the new CRT version, but the per-user is a true per-user for 3.5 (and when the new CRT is already installed via normal Windows Updates, you won't even be prompted).

@J. Morton: I appreciate the suggestion of only supporting per-user installs, and I'm heading towards that position. It won't be changing for 2.7 or 3.4 at this stage, but I do plan to discuss exactly this issue soon with the core team and figure out what we're actually trying to achieve with our installers.

I would never suggest that somebody build Python themselves unless they are a distribution, and ISTM that even on Windows, 99% of Python users should be getting a distribution rather than the python.org installers. (Which makes the python.org installers fairly redundant, hence my plans to discuss what they should be trying to achieve.)

The /a "install" is not a real installation, and though it "works", it isn't necessarily supported. (It's actually a transformation of the MSI file to separate the files to install from the installer - you should see the MSI file get considerably smaller after you run that command.) In particular, the py.exe launcher is not going to work, and many other programs that automatically detect Python will also fail.

Not sure what you mean about "compatible with PyDev/Eclipse". It's their responsibility to be compatible with Python (and I say this as the lead developer of Python Tools for Visual Studio, where we've pulled all sorts of tricks to remain compatible with Python :) ).