A customer came to me with a question: they no longer saw the “Size” column in the Programs and Features list (where you go to modify or uninstall software) on Windows 7 when the installer was not an MSI.
Here’s the story: we used to run some heuristics, as described here: http://blogs.msdn.com/b/oldnewthing/archive/2004/07/09/178342.aspx
However, if you read through those heuristics, you can see that they’re not exactly the most precise, and in general it’s often better to not say anything than to say something wrong. So, the article then went on to suggest that you populate the EstimatedSize value in the Uninstall registry key to avoid the guessing.
Which, of course, had one problem: we didn’t always look there if the application wasn’t installed by an MSI. (A web search will find some of the clever workaround that people have discovered to get ARP to look there.)
For Windows 7, we fixed that problem: we now look at the EstimatedSize value for any application on the system. Furthermore, we removed the heuristics altogether (they were pretty hacky) and only look at the EstimatedSize value.
Conveniently, the customer who brought this up happens to make programs which are used to create application installers. They’re big enough that I’m pretty sure you know their name. So, my guess is that they’re going to start writing that value in any non-MSI installers which aren’t doing so today.