I think it does sometimes but not always... like when John Scott moved his forums to a new domain they took a bit of a hit. also 301 redirects surely will get abused a bunch more going forward. I think on same domain they should have a tendany to usually do fine but some cross domain ones might not pass their full value. I do not have much experience with 301s though
I've seen people report mixed results with using 301s. I highly recommend that you 301 redirect example.com to www.example.com on all your sites. But as far as a totally different domain, I would only do it as a last resort.