Once I'd decided to buy a DSLR, the obvious choice was a Canon EOS 300D. It was the cheapest DSLR; it could use the two EF lenses from my girlfriend's film EOS; and I have friends who work for Canon and who might have been able to borrow interesting lenses. I had a chance to use the Canon 300D on a bushwalk and it was pretty good.
However there was no lens for this that fitted my "one lens for a luggable hiking kit" requirement well. The 18-55mm EF-S kit lens had reasonable closeup capability (0.45x effective magnification) but was a bit short, by some accounts not particularly sharp, and not as solidly built as I'd like for taking bush. The 17-85mm EF-S lens had the perfect range, but had lousy magnification and would have blown out the cost.
Olympus' 14-54mm f/2.8-3.5 lens, with a 35mm equivalent reach of 28-108mm and magnification of 0.5x, was just what I wanted.
I was first attracted to the Four Thirds system because of the idea: a system built for digital, with a smaller sensor and lenses designed for that sensor. At least in principle this offered smaller and lighter lenses (especially telephoto); it would also offer better macro magnification and greater depth-of-field.
The E1 seemed out of my reach entirely -- too expensive -- so I was waiting on the Olympus E300 before deciding between that and the Canon 300D. But then the E1 prices started dropping... The weatherproofing was a big drawcard (along with the dust-shaker). And I had a play with the E1 in a shop and it felt really nice.