Could someone give me an example of a "sandbox"?

A sandbox is a place where you send people who try to drive developers nuts. Developers have enough to do.

 

Yes, I perfectly understand that. But there is one thing here:
1. If I start to cut off security-related staff, it will decrease security level of the users. "Some protection means no protection at all" (C) by me.
2. If I start to cut off some interface-related staff, there will be no reasons to buy Pro version as a free one gives a highest protection level.

Also, I just see at GiveAwayOfTheDay migration results. Well, they are not really impressive at all. The only way I can increase the revenue is to bundle a search engine's toolbar into the package of free version of the product.

 

The free model works best when the publisher has a bunch of pay only products and the free one is being used as advertising to get people in the door. Comodo is a good example of this.

The reduced features free model is somewhat risky for the publisher for exactly the reasons Ilya explains. I really think its bad form to bug a developer about this. If he makes the wrong guess he can't buy groceries.

Another possible approach is to use the free model to accelerate development, ultimately switching to paid. This is what Jetico did with their firewall. I suspect this might be the case with Threatfire, but time will tell. These companies also have other paid products to live off of.

A handful of programmers have successfully used the free model to build their reputations in order to get jobs related to what they were doing, in some cases selling the project to their new employer. I seem to recall this was the story on DVD Shrink.