At the beginning of the year, a large UK SEO agency was banned from Google for a short period of time (a few days) - for spamming! It was big news as they regularly touted their "ethical" approach to SEO and they have a lot of big brand clients, so it was covered on most major SEO forums / blogs.
Now, a brand search for the company - aside from the top slot and a couple of PR releases, the entire SERPs are filled with <company> banned from Google for spamming! Not a great situation when you have big brand clients or investors carrying out due diligence.
What's more, it's got to the point that they are *trying* to protect their name by pushing those listings from the top 10 or so by optimising other pages for their brand term - ranging from recruitment listings (one of their other SEO websites actually links to a SEW recruitment thread rather than their own vacancies page in an aim to get it ranking higher than the ban thread!) to creating "optimised" articles that link to other businesses with similar names (to get them ranking in the top 10).
What's funny is that despite how much they have tried to clean things up, Google still displays the negative publicity for brand searches. (ironically it has been speculated that the company anonymously created the publicity themselves for the link loving!

)
So is risking your well established brand and multi million pound client base worth a few links and some traffic? I'd say no. But it depends on how you do it - are your users (ie potential customers) likely to read the negative comments and be put off by them?
I once had one of my sites reviewed by Harvard Business School - they complimented the uniqueness of the site, but slated my spelling!

I wasn't bothered though - that had more benefits that negatives.
MG