It's not an automatic back-button press for me (I mean, hell, most sites do that these days), but I do find pages that yell at me to BUY IT! first thing to be really gross. Like having a salesman run up to me on the street, pen and contract in hand, yelling BUY BUY BUY! Like, WTF. I don't know you, and I don't even know what you're selling yet, but you're shoving a contract in my face already? "Crass" is too mild a term.

The only time it's convenient to have those buttons front and center, and the only time I click them very soon after first visiting a site, is when I already know what the service is and I'm at least 90% sure I'm buying it before I even load the site (tenth visit, already used the service at a previous company, buying a product/account for a family member, that kind of thing)