Good blog, and interesting link, thanks! I will add that to my list of work procrastination tools.
Interesting about temperature though as my legs definitely go better on warm sunny days - although that may just be coz I get all excited about being out in decent weather for once...
A bit of all three, plus temperature would seem to be the consensus
http://alex-cycle.blogspot.co.uk/2009/01/turbocharged-training.html