dpreview and a few other sites (this forum, for example) influenced my first DSLR purchase, simply because I was so out of the loop I had to rely heavily on a mix of feature information and people's opinions about it. My last SLR before that was a fully manual, fully mechanical body that could operate without a battery.
Since then, my purchases have been based more on which features of my camera I genuinly use and find useful, and which features I wish to improve. I'll give you a few examples.
My first DSLR was a Pentax K100D Super. I chose it in part because my film body was a Pentax and I had some Pentax glass from way back when. Pentax never changed their mount when they added AF, so old lenses are still useable with some extra work. I also chose it because in the back of my mind I knew I would eventually want somehing newer (I'm a techy and a gadgeteer, what can I say) and I wanted to drag my old man into the world of digital photography, something he has been unwilling and unable to spend money on.
I learened quickly that the K100D Super was too small for my hands. It was a lovely camera, did everything I wanted at the time, but after a day of working it my hands were in pain. In particular, the arrangement of the front wheel below the shutter button is uncomfortable for me (same with the Nikons) - it just doesn't fit my hands. So I picked up a Canon 40D, a camera that I found comfortable to use, despite the increased weight, and liked using.
Sadly the 40D got nicked, so I replaced it with the slightly newer but mostly identical 50D. I never wanted to upgrade to the 50D, in fact, I was thinking of picking up a second hand 30D, since the 40D on the 2nd market was still too expensive. But I came across a good deal for the 50D+18-200mm IS, so I took it. The 50D had a higher resolution sensor, could do higher ISO while retaining better colour - skin tones in particular - but also had more noise. I used it for a year and half, and by that time I had started to shoot more live music and events. One killer feature of the 7D is that it can have different AF settings for different orientation, i.e. you can have one configuration for landscape and a different for portrait. It remembers selected AF points (if you're using manual select), so as you flip back and forth, the AF is ready for you. The lack of this grated me on the 50D, in particular when using the grip, because there's no AF button on it, and I had to manually change AF point each time I turn the camera. So this was one reason I got the 7D.
The other reason was much better colour and lower noise at high ISO and in low and poorer light conditions. This is useful for music/events, but I was also interested in doing some stars while travelling in places that don't have clouds all the time. Someone on the dpreview.com forums that had both the 50D and 7D was kind enough to set up a night stars shot at high ISO (short shutter so we don't get trails) with all other factors being the same, and send me the raw files so I could see for myself. Turns out the 7D destroys the 50D in this regard, and since I was about to leave for SA for two weeks, this was all I needed to swing it for me.
Now, you may ask why I never went for the 5D/5D2 if I was after better high ISO performance? On paper, and in the reviews it looks like a better camera all round. But it missed key features that I had and was after. Its Auto ISO function (which I find incredibly useful) is even more brain-dead than on the 50D and 7D. But more importantly Its AF isn't even in the same class as the 50D, much less the 7D. Only the center point is cross-type and sensitive at f/2.8, the surrounding AF points are clustered so close to the center, they're essentially useless. Just read the 5D forums on dpreview and see how many 5D shooters swear by the center-point-focus-recompose method. They'll swear it's the best way to do it, but it's really the only way to work with the limitations of that system. This is a deal-breaker for me.
So, you can see how the reviews and information sheets are of limited use. It's important to be informed, but you also need to have a good sense of what you have and what you use and how you're looking to improve on that.
