I definately find I drive more conservatively, sometimes even if I'm ahead of someone and I know I break early for a particular corner, ill tap the breaks to give them a heads up. I also find I drive more aggressively if I know I'm the fastest guy on the track, as I feel frustrated if I'm not leading - if I'm not the fastest fella, I drive more carefully to gain respect of my peers haha
Also, does anybody else pull a strange face if they can forsee a tap coming up? For whatever reason I find myself pulling a face instead of breaking, somehow believing this will magically stop me!
I'm the same, I definitely drive more conservatively online.
I did two contrasting races recently;
Laguna Seca: Started first, beat off the line by someone who turned out to be slower. I back off on the exit to turn one to avoid hitting him off, then two cars take me on the inside of the first of the 90 degree right handers. Then I get sandwiched between two cars for the next turn and lose several more places. By the corkscrew I was 8th and the turn afterwards I got rammed off the road (Again trying not to hit the car infront who braked hard, which is unusual for that corner). I eventually finished 9th, and the guy I avoided hitting into turn one finished 13th, and last. This could all have been avoided if i'd just pushed my way past the slow car into turn one, It was a shuffle race and I was in a decent car so I probably would have led the entire race.
London: Time after time at London i'm far and away the fastest guy on the track. I do drive conservatively on this track and that is how you win here. I started last and kept braking early for each turn, cutting the kerb into each of the tight turns (Still counts as track). Other cars would brake later and venture wide or get a slower exit. So one by one I kept picking them off, not making contact with any of them until i'm first, and then I go on to win the race by 4+ seconds. Driving conservatively here pays it's dividends because there are no obvious places where you have to back off to avoid contact, or where you can be punted off (Providing you go as close to the barrier as possible on the inside of turns).
It varies from track to track, race to race and the skill of the competition. But I pride myself on building a reputation for being a clean driver. If you're faster, be patient and you will pass. If you're not, try and keep up and make sure not to punt him off. If avoiding contact infront results in you losing places, hard luck, it happens to the best drivers in the world too. I do get impatient if I know I am faster though, and do tend to be more optimistic with my passing moves, hoping the slower driver will go wide anyway.
Oh, and I definitely pull that face when i'm bracing for impact, I didn't realise until you mentioned it, but I definitely do it
I also tighten the muscles in my whole body when understeering round a sharp corner, as if it will make me suddenly gain more grip. 
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