I wanted a place to discuss some thoughts regarding layout switching, how we do it, and some possible alternatives. Specifically, when Qwerty still needs to be available in case a co-worker, SO, child, etc. needs to use your PC for a minute.
The obvious path of least resistance is to remap the keys at the OS level. This is easy to do and can be changed on the fly. But on my Windows PCs, I have found that if I leave the US layout enabled, the system seems to occasionally "decide" to switch back. Also, at least back in Windows XP, the layout was application-specific, so you might switch apps and discover that the layout had changed.
Currently, on my W8.1 laptop, I have discovered that Ctrl+Shift (without hitting another key) switches layouts. Odd, because the only shortcut mentioned in the Control Panel is Win+Space. It happens to me a lot when browsing, I want to un-close a tab with Ctrl-Shift-T, but I change my mind, so I release shift and BAM, layout change. Then Ctrl-T for a new tab, but it now sees Ctrl-K and gives me a search prompt.
Another option I've used is
DvAssist, but it hasn't been updated and doesn't always play well with my W7 desktop at work. I like having a tray icon that I can double-click to change layouts when needed, instead of having a keyboard shortcut that can be accidentally activated.
There's also the option (on Windows) of remapping keys in the registry, usually through a frontend like
KeyTweak. That's currently how I'm accomplishing a few key swaps, like RAlt -> Win on my Model M, and Esc <-> Backtick and Backspace <-> Backslash. The downside to those is that there are no on-the-fly changes, as the system reads the keymap from the registry on boot.
Neither of those software mapping solutions work in a pre-OS environment such as a rescue situation. Now, generally, you won't be typing out anything significant and that won't really matter. But still.
Of course, what may be the best solution is remapping in hardware. I have a WASD V2 coming on Wednesday, with a Dvorak DIN switch. I'm also looking forward to the Pok3r for the same reason. But if I undo my software map, I lose the ability to switch layouts for others, at least not without (possibly) disconnecting the keyboard, flipping it over, figuring out which switch is for Dvorak, etc.
Once I have a hardware Dvorak board at work, I may keep a Qwerty board plugged in and available. That would solve it, and it would have the added benefit of giving me an excuse to have more keyboards sitting on my desk.

Perhaps I could make (or maybe someone already has?) an AHK Dv -> Qw converter to leave any current mappings alone, whether they're hardware or software, but run this one exe to begin mapping keys out to standard. For me, at least, it's very seldom that others need to use my PCs, so that would be a workable solution.
Sorry, this is a bit rambly. Just wanted to get some thoughts out.