A Cre8asite Forums thread asks if having too many 301 redirects from OLD site to NEW site can hurt you in the search results. It is a good question, one which administrator Ammon Johns (aka Black_Knight) comes out to answer.
You have legitimately moved the content to a consolidated main site, so it really shouldn't be an issue. Of course, ideally all the deep-urls from the scattered old sites should be redirecting to the specific page where the rquivalent content now resides on he main domain. Deep URLs from the old domain should really not all be pointing at the homepage as it is just poor usability, and poor usability is something the engines don't mind devaluing.
If I were a search engineer, I wouldn't be worried about the number of sites redirecting to the new site, but I'd have built a lot of warn-levels into the algorithm for when all the deep-pages of many different domains were pointed solely at a homepage. That would look like any made-up url on the old domain would give a 301 redirect, and that is an issue my algorithm would have to discount completely.
I agree. When moving from an old site to a new site, the best thing one can do is 301 redirect all the deep old pages to the new respective and related deep pages on the new site. So you can have thousands of redirects. In fact, when we tear down and old site and rebuild it. Normally, we are able to map the OLD URLs to the new URLs using some smart scripts. That builds thousands and sometimes infinite 301 redirects. Why infinite? Many sites we take on may have infinite URLs because of tracking; i.e. domain.com/page1.html?trackingurl=23322, etc or even because of session IDs. We redirect them all, automatically. So, potentially, we redirect an infinite number of OLD URLs to NEW URLs using 301s.
Forum discussion at Cre8asite Forums.