I agree to a great extent @
bpcyclist. Especially early-on, when I was just getting into cycling, I really didn't know what I liked, how I would be riding, etc. It was all new to me which led to some impulse purchases. Now, even though I'm just approaching the half-year mark, I've ridden over 2000 miles, a lot of it really pushing myself and varying up my rides (some intra-city, some outside on long paths with no stops, hills, flats, etc.). Now I have a very good idea of what I'm looking for in a bike.
True, a quick 10 minute ride near the LBS isn't going to simulate that, but my early impulse purchases (and one mistake) has allowed me to build relationships with a few LBSs that carry different manufacturers, and would let me use a bike for an extended time. Maybe not a week, but for a decent amount of time. And those LBSs are near where I do a lot of riding, with some challenging stretches, so I could really put a new bike through its paces.
However, the TCR and S3 has really cooled my impulse purchasing. They're both such a blast to ride, that if I even do test out a bike, it's more for curiosity rather than serious purchasing intent. Don't get me wrong, if some make/model were to knock my socks off, I would be tempted, but these two bikes...and the TCR especially...are highly rated and respected models. They may not be everything to everyone, but they tick off just about all of the boxes in terms of what I'm looking for in a ride.