The ideomotor effect known in psychology circles as a form of priming, or "influencing an action by an idea"1. Priming has the effect of altering your actions without you knowing about it. The theory has been tested many times over in different forms of experiment design.
Psychologists have observed that when subjects are primed for something positive that tasks become easier to complete and subjects can complete a task better. In the examples below, the design was intended to prime the user with positive feelings to make the task of signing up easier.
The action that is being primed is to sign up for the product. The priming being done is to relax the user with an image then direct to the user to a nearby form.
Good design has picked up on the importance of these psychological tendencies, implemented them well and with proven results.
This is not flat or minimalist design trends with a lack of complex aesthetics. The design implementations are based upon proven effects and backed by the companys' own conversion testing.
Basecamp, the original flagship product at 37signals did this a few years ago with great results.
There are several interesting design elements going on here, though, in terms of priming, there is one common element that puts the user at ease and ready to complete the short form; the person staring straight at the user with a smile.
Highrise, the Basecamp-like product for CRM, has also received similar attention to improve conversion rates for the products landing page. The design slightly different with rotating images of people, all relaying subtle cues about the product.
Shopify had a slightly different implementation on this design style. The person is even more happy and looks to be taking action on their business on an iPad (perhaps suggesting their business can be run on an iPad if you use Shopify). This seems to be a good adjustment for a seemingly daunting task of setting up an online store.
Square flipped things around and isn't showing a person smiling at all. They're showing the merchant finishing a sale at a market. This says "it's very easy" and with all the basic information about rates right under the form, Sqaure has made the barrier to sign up very low.
Not Sure What They Were Thinking
Twitter could learn from the other companies in this post and try something other than landscape or party photos. Tweeting isn't just about the masses bombarding the Internet with their short thoughts. It's a personal experience that everyone can enjoy.
Twitter should try out some different landing pages. Though, I suspect people don't sign up to Twitter after going to the homepage, it's usually all the companies that give it free press that do the job for them.
Even More Arrogant and Downright Lazy
There's no subconscious immediate emotional design here. Facebook is so ubiquitous that people either want it or they don't. I suppose I understand there complete lack of emotional design.
What Have We Learned?
That we don't need to use fancy design elements as much anymore. The Internet is more mature and should mimic more of Don Drapers messages about conveying strong emotional connections (like nastalgia).
All of these designs use space well, meaningful colors and clear readable text. Good web design is more about clarity than it is aesthetics.
1 Thinking Fast And Slow, Kahneman, 2011