Run OSX as normal off external HD? I'm continuing to hatch a plan to keep running whilst emergency repairs are carried out on my MBP. Further to a question I posted on Monday I'd like to know if anyone could shed light on whether this is possible.

Can I take my MBP drive out, put it in a caddy, plug it in to an iMac and boot my drive via the external then run it as a normal setup? I understand this might run slower, hopefully not too much. The main thing though is to not have to break from routine for long to get things up and running (owing to a huge deadline a week out that my laptop is too unstable to meet).
Yes: This is totally possible 
and you should not have any problems at all.

You should consider though, that every Mac has a minimum and a maximum OS X Version which is officially supported.