Are they worth anything, if they are from relevant sites?  I'm I better off avoiding linking back wherever possible?

I need to migrate a wordpress site from domainname.com to domainname.co.uk. If I just put a 301 on every page on the .com will that cover it? Would it make sense to go and change all the backlinks/profile links to the new .co.uk site or doesn't it matter if you have a 301 redirect on it? Thanks

What are your thoughts on SEOs and web designers putting their own links in the footers of client sites. For the sake of argument, lets assume that the client is happy for the link to be there. I'm referring to the SEO merits of the link being there from an 'irrelevant' website. My belief is that this goes against what Google is looking for and that these are irrelevant links and likely to be picked up and penalised.  That's what I believe! However, I see lots of sites offering SEO services that have dofollow links from their client sites, using exact match anchor text and they are all ranking highly. Is it just a matter of time before Google sniffs them out and penalises them for it?  Or should I be going through my client sites and adding myself a dofollow link in the footer? (with their permission of course). The highest ranking sites in any UK city do this.  If you search SEO Manchester, SEO Leeds etc and find the top ranking sites and check them out on opensite explorer, they are all using a disproportionate amount of dofollow backlinks form client sites.