How to automatically update NuGet packages to latest available version
You could probably leverage the NuGet Package Restore feature (a bit of info here : http://docs.nuget.org/docs/workflows/using-nuget-without-committing-packages)
At project build, it calls "nuget.exe -install" to reinstall the packages from packages.config. I haven't tried it but you could add a Update command to the nuget.targets file in the same way. (You'd have to call both nuget.exe update and the existing nuget.exe install).