Does Windows 7 have .NET 4 installed by default?

Windows 7 does not come with .NET 4 preloaded, but if you run Windows Update to get it up to date, it will be installed.

UPDATE:

Checking my update history over again, and yes it's offered as an update, but only after I updated the computer to SP1.

Windows 7 (SP1) comes with the following .NET frameworks 1.0, 1.1, 2.0, 3.0 and 3.5 support AFAIK. If you need .NET Framework 4.0 support then your clients need to download at least Microsoft .NET Framework 4 client profile.

I have just verified Windows update on a clean Windows 7 Home Premium installation. Directly after installation, Windows Update offers a security update for .NET Framework 3.5.1. But no .NET Framework 4.0 is offered by Windows Update at first run of Windows Update. I am going to install the patches provided first and then report if .NET Framework 4.0 is offered at a later stage.

Update: I just entered the second update round on my VM, and now I am offered six important updates only. Still no .NET framework 4.

Update 2: I just had to do another two rounds of Windows Updates and now "Microsoft .NET Framework 4 Client Profile for Windows 7" is provided through Windows Update.

So yes, it seems to be automatically deployed if Windows Update is enabled. Either you need to make sure really all updates are applied or you just go for the download link provided above.