If you think about it, what you are suggesting has some sort of "usability" built into it - (lawyer give the accountant a plug when discussing minimizing taxes on his blog).
The problem with a network is that it eventually creates patterns. So if you think about BuildMyRank network of sites. Let's say they had 1000 Blogs B1-B1000. Now let's say they have 100 clients buying 10 links each C1-C100. If you graph it out, you'll notice the links will develop a pattern, which is fine (to some extent).
The problem lies when the content is completely unrelated to 1 another within 1 blog. Also, every blog post is linking to atleast 1 external site. Further, a network that size would certainly have some level of overlaps in terms of Web Hosting, IPs, Class C's, Domain Registrars and so on.
When you do it only to tweak search results (and we all know we need links to rank), it always contains some element of risk. However, I would suggest you do it more with Brand Keywords rather then exact match with your keywords. So if it's ABC Law Firm you are linking to, let it be ABC Law Firm as the anchor text vs Los Angeles Personal Injury Lawyer. Mix and match, maybe even nofollow them. And as I have said several times in my posts, don't overdo any 1 kind of link building. A natural link profile consists of 100'd of different kinds of links, varying anchor texts and so on.
I hope that helps.