1. Long boot times. This gets worse as your recipes get beefier.
2. Same script, different results. Running your recipe next year might not yield the same result (e.g. if you don't specify a precise version of a package to install).
2. You can version server templates to use specific revisions of RightScripts and recipes. In fact, the Chef implementation is built around using a branch or commit SHA1 to specify what versions of the recipes you want to use from your repository.
disclaimer: I work for RightScale
2. I think it's always important to be explicit about, and have backups, of the packages used in these scripts.