Hando - rolling it on the spine is correct. Some people take it off and slap it down again, like in old movies - looks and sounds good, Mastro Livi does the same. If you aren't doing it quick enough it can have a detrimental effect on the blade - there is a minimum speed. Too much draw (strop resistance, caused by over-conditioning the strop) can also blunt the blade. You should be stropping for 20 or 30 laps after the shave (dries the edge and maybe some of the oils from the strop leave a protective film - maybe!) and again for 40 - 60 pre-shave. If you have rolled the edge, it will have to be honed again - have a look at it under a strong eye loupe. Maybe you have over-stropped (very hard to do - not sure if it is even posible) and a second strop pasted with chrome oxide is called for? If you don't want to invest in a second strop, newsprint stretched over a flat surface (plate glass/marble) will do, or a slab of balsa. CrOx acts like an ultra-fine hone.
Colin: interesting observation. When its cold the hairs stand up more, away from the skin (I remember reading about a female impersonator who shaved once with hot water, then again with cold water - said it brought the bristles further out of the skin) so maybe if it is humid and clammy your skin stands proud of the bristles then when you cool down it recedes and leaves the bristles proud? I don't really know - just speculation. Maybe if you are too hot your skin stops the razor from gliding? Interesting.
All the Best,
Neil.