I currently use the awesome Module::Install as an integral part of my development and deployment tool-chain. What this does for me is make it easy to not worry about my project dependencies, nor my target deployment box. It makes it easy for a group of developers working on the same project to keep well in sync with each other regarding dependencies. Although it does have its detractors I think it has far and away become the favored installer of modern Perl developers.
One thing that is troubling me is whether or not to check in to my repository that "inc" directory that gets created (along with the pile of required Module::Install files as well as any extra plugins you my have installed) when you run "perl Makefile.PL" on a Module::Install enabled Makefile.PL script. In the past I have not, but lately I've seen quite a few projects on github that have. I can see the upside, since checking in those files would make it easier for another person to checkout your code and just get to work, if that 'inc' is missing you may have to install Module::Install and whatever other plugins you favor, which has been a bit of a gotcha for some of my newbie developers.
On the other hand if I do check that stuff in I might end up with extreme version lag behind Module::Install releases and that increases my risk of regressions when I do upgrade.
So... What are you all doing? Do you checkin inc or not? Why?