On one hand, people leave bogus emails just to get the download link. You don't get any means of contacting them afterwards or build your email list.
On the other hand, if people see that sending an email to get a trial version, they might not even bother at all.
Which is an optimal choice? I am a bit worried because I am seeing downloads but very little contact or purchases.
When I used to run a service website, I was used to getting a lead for work at least everyday in my inbox.
Now I am running a software for purchase website, I am seeing notification for downloads, but otherwise silence. This is kind of irritating because I don't know what needs to be optimized, my software, the price, the website? How long does it take for someone to get to using the full paid version?
I can see the latter is also quite expensive. At the rate it's going, it will cost more to acquire a paying customer for a software than a paying customer for a programming job.
The only way to find out what works for you and what does not is A/B testing. For instance, display the registration form on odd dates and direct downloads on even dates for two of four weeks. You will then learn how many downloads you would lose because of the registration form.
IMPORTANT: If you sell internationally, make sure to break down the registrations by country. You may find that visitors from countries you seldom or never sell to are more likely to fill the form, usually with disposable email addresses, whereas the visitors from your key markets are more likely to leave your Web site when they realize that there is no direct download.
You may A/B test everything, from calls to action to web page layouts to prices. Patrick McKenzie's blog is a great source of information on that subject and s/w business in general.
While it depends on the product, generally requiring an email address for a download decreases the number of people who download your software. For expensive business software (say > $100), this may not be much of a problem. The decrease in the number of downloads is less and the quailty of the potential customer is higher. For low priced consumer products it definitely is a problem. By the way, if you require an email address, you email them a download link- so the email address has to be valid.
A better question is- How do you know your web site and trial product are working correctly? Have you tried using a computer that has never been to your web site, or had your program installed on it? Download your trial on a fresh machine and see if the trial version works as it is supposed to. And does your web site work properly in IE, FF, Chrome, and Opera?
Next, do you have the proper incentives in the trial version to convert that tiral into a sale? Why should the potential customer buy, and how do you inform him about buying? Does your trial software have good purchase incentives?
Have you checked your competition? How do their web sites compare to yours? What about their prices vs yours? And what do their trials look like?
Finally, what about your web site usability? Get a friend who has never seen your web site or product. Tell him the url and ask him to find, download, and install your product. Sit down and watch him as he goes to your web site and without any prompting from you, finds and downloads your software, then installs it. How did that process go?
When looking for a particular type of product, there's typically more than one option out there. That makes it easy to eliminate the ones that make you contact them and/or register to download a trial. Companies with secretive and manipulative tendencies drive potential customers to the competition.
Just be transparent. Make it as easy as possible for customers to evaluate your product. Also make it easy for them to buy it. Don't operate in too small a niche otherwise you'll need to have ridiculously high pricing and that will turn off potential customers. High pricing also means you'll need to spend a boatload of money on sales and, even if you can afford it, it's too risky when you're starting out.
The simple answer to me is not if you have to require one route or the other to receive your product, but is your product so incredibly good that it sells itself. What I mean is if you look at Mailchimp for instance, after you use it once you realize how great it is and you tell your friends about it.
More than focusing on which way to "hook" users emails, focus on creating awesome content and an incredible user experience.
As for revenue models I would recommend a lot of research on the Freemium model. If you study companies like Dropbox, Mailchimp, Wufoo, and others like this you'll see a trend. Great products, that users feel good about using, and have no problem upgrading to paid version as they need them.