I'd been diagnosed with PCOS so I didn't really think there was much chance of me 'falling' pregnant without lots of planning. After coming off the pill we made sure not to get me pregnant until I'd had a couple of periods and then just carried on as normal. We didn't worry about timing or lying still for half an hour after sex or anything and when people asked if we were trying I kept saying 'well we're not doing anything to prevent it, but we're not exactly trying.' So I was somewhat flabberghasted to find I was pregnant after just a couple of months. I'm still not quite sure I believe it ;o)
So, yeah, I beleive that not trying is the way to go. And you hear so many stories of people who tried for years and then gave up and adopted or splashed out on flash cars or extravagent holidays and then 'bingo!'