Following these instructions as best I can, the VS 2010 Shell Extension Manager turns up no results when searching for "nuget". The only deviation as far as I can tell is that the instructions show using VS 2010 Ultimate, and I am using the Shell. I had no problem with AnkhSvn and I can see all kinds of other extensions in the Online Gallery. One other thing, before attempting this I installed the NuGetPackageExplorer (not even really sure what it is, just trying to get off the ground with NuGet and I found it on their CodePlex download site -- ultimately I'd like to publish my own NuGet package, since someone suggested it to me and I've heard about it a couple other times). Any Ideas?
Update
I recently got a new computer (Windows 7 64 bit) and freshly installed Visual Studio 2010 Shell and F# 2.0 and am having the same exact issue. Note: I just checked the About page and it says the only installed component is Visual Web Developer 2010 (seemed odd to me).
Edit: Check what's selected in the left pane of the Extensions Manager. It defaulted to "Installed Extensions" for me, that could be your problem. Select "Online Gallery -> All" then do the search again.
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Not sure why it's not showing up, but you can install NuGet by going to the website and clicking the blue "Install NuGet" button. This will take you through to a download page for the latest version (1.3).