In the first page of evernote two text boxes are shown, one for email and the other one for password. And I almost always get these mistaken for the login form! I enter my credentials and then realize that I should have gone to the login page first! So to me, it seems very wrong for the first page to be the signup page. Why have they designed their first page like this? What's the philosophy behind that?
I had to go and check this out for myself to make sure:
If you are completely logged out when you visit the site, their assumption is that you are completely new to Evernote - Facebook takes a similar approach; if you're not logged in you get a page that is more biased towards 'sign up' than 'sign in'.
However, if you have already signed up (with that particular browser on that particular machine) then, if you close the window and then revisit the site in a new window, you get an 'upgrade' page instead. The assumption here is that you already have the basic product, maybe you'd like the advanced version.
To add to what Andrew has said ... I've always wondered why we don't more often set up sign up/log in pages to be "smarter". If you're using a browser or machine you've never used to visit the site before, you'd get the sign up function, with a much smaller "Already a member, sign in" link as a second option.
If you have signed up, and are revisiting the site to log in, the browser should know (cookie) that you are a member, and show you primarily the log in function, with a much smaller "New? Sign up" link as the second option. Or, as Andrew suggested, maybe a sign in AND upgrade offer (if applicable).
Shouldn't the sign up/log in page know if we've registered and show us the applicable choice?
I think it is not "very wrong" as you mention to have signup section in the first page. In business perspective, in order to gain more customers, they will induce everyone's attention by placing the "sign up" form in the centre of the page. This is given the higher priority than anyone else who visits the site. Once you are signed up, your attention towards the signup form reduces and eventually, you look out for "Login" link in the page. Based on your frequency of visit, you will get used to the place where to sign in. This approach is used to ease the process of signing up without a second thought.