+Mark Lentczner +Vincent Hanquez
As long as the HP stays the way it is now, I don't think people will stick to it. I believe it has literally been years since I've used it. The only time I use it is for bootstrapping cabal-install, which only seems to happen when I build a brand new system (and even then not always since distro packages may do it for me). Once I have a recent enough version of cabal-install, I use it exclusively and the HP ceases to be relevant for me. It might be relevant in a much grander view of compatibility, but my concern is to make sure my packages build when someone types "cabal install snap", and to fix them when someone complains that they don't install.
I think the only way the HP will have more adherence and impact is if it becomes much more intimately related to cabal-install, hackage, and the standard way people install Haskell packages. For instance, if the HP existed as a separate "production" instance of hackage, then I could see it having a lot more impact. I could envision doing something like...
$ cabal use production
...to restrict oneself to the HP repository. And then...
$ cabal use testing
...to switch to the bleeding edge (what's currently in hackage).
I don't mean to minimize the value of the work being done on the HP, but I think that as long as it is relatively invisible in the everyday life of prolific Haskell developers, people won't restrict themselves to it.