I've had an ecommerce site for 5 years - I offer downloads, nothing tangible.
I've always linked my ads to the homepage. It's just one service I offer and it's never seemed logical to link to "landing pages".
I've done a LOT of A/B and multivariate testing using adwords tools and have got my "conversion" rate from 8% 2 years ago up to 16-20% now...where a "conversion" counts as someone clicking through to the "Sign Up" page.
I got to thinking this week - would it be worth it to link all my adwords ads straight to the sign up page. I imagine everyone landing there would have to go clicking around the site to see what it was all about anyway. Has anyone had success with this policy? It seems a bit pushy to me - like getting someone coming into a store, pushing them straight to the cash desk and saying "wait there, we'll get the products you want and bring them to you."
I suppose I could always try for a month and see what happens....
Although I do not have experience of doing this myself, as a user I would be put off if I had to do some hunting around to "see what it was all about". When it is so easy to just click the back button you want to let visitors know what they are looking at straight away. Of course this could be different in your industry so A/B testing would be an ideal way to find out for sure - but I would be worried about people bouncing.
How about some sort of hybrid sign up page? - where they are given some landing information before being promoted to enter their details. This could be a good middle ground and perhaps something to include in your multivariate testing.