How do I - Determine what type of site template was used when a SharePoint site was created?

If you work in SharePoint regularly, you may develop the ability to look at a SharePoint site and correctly guess which template was used in the creation of said site.  Of course, given how SharePoint works, you'd probably only have a 50/50 shot at best of actually being correct.  Given how most everything is connected to Features and the fact that site templates in most cases just have a given sub set of Features that are turned on during the creation process, it's really anybody's guess.
Powershell to the rescue!
Of course, if you're an administrator with shell access to your farm, you can always resort to Powershell to get that answer.  All you have to do is get the WebTemplate property of the SPWeb object for the site thus:

Write-Host (Get-SPWeb http://sharepoint.crayveon.com/sites/site123 | Select WebTemplate);

Alternatively, you could use the Get-SPSite cmdlet at the beginning of the pipe to get all the sites and sub sites and their templates thus:

Write-Host (Get-SPSite http://sharepoint.crayveon.com/sites/site123 | Get-SPWeb | Select URL, WebTemplate);

Enjoy

C