I've updated my .NET Availability and Viability With Portable Apps statistical and functional analysis with the latest info and worldwide OS stats. The news is a bit mixed for fans of .NET and .NET-based apps who like to use portable software.
While Windows XP has been end-of-lifed and most folks in many more prosperous countries won't encounter it anymore, it's still holding with over 25% of Windows installs. So, some folks will still have to deal with it on a regular basis.
Even discounting that, Microsoft's decision to disable .NET 2.0, 3.0, and 3.5 (and discontinue 1.0/1.1 entirely) on Windows 8, 8.1 and 8.1 update 1 will throw a major wrench into the lives of anyone expecting their .NET portable apps to work everywhere. On Windows 8 and up, .NET 4.5 is installed by default, which is a good thing for .NET fans. But... and there is a BIG but here... Microsoft decided that nothing below 4.0 will be supported by default unless an administrator goes in and manually enables earlier .NET versions.
As an example, this means that while your handy zipped version of KeePass 2.0 will work out of the box on Windows Vista and Windows 7, it won't work on any Windows 8 boxes unless the admin has gone in and manually enabled it after the OS was installed. (UPDATE: As noted below, I was incorrect. KeePass 2 is specifically configured to work on .NET 4/4.5 as well.) So, basically, you can forget about universal portable app support for .NET. We'll need to check and see what .NET version the app needs and whether it's installed and/or enabled on a give PC before launching still.
So, what does this mean for .NET on PortableApps.com? It means nothing changes from our original plan. The PA.c Format already includes a line to indicate which version of .NET an app needs (if it needs it). And the platform will be updated in the near future to automatically read that and check for it, either greying out or hiding apps that won't run on the current PC. As planned, we'll be officially releasing .NET-based apps, but we'll be relegating them to a separate section of the app directory that users can choose to enable or disable based on whether they want to deal with .NET uncertainties.
UPDATE - Thanks to winterblood pointing out that .NET apps can be set to support multiple runtimes. While this doesn't change the base percentage of what .NET frameworks run where (my original linked article), it does change the percentages of where a give app will run. This does open up the possibility of us including .NET apps broadly. Read my response below for more details.