I think some people are missing the point here.
Buying links is not a bad thing as long as they are relevant. Lets face it there are 4 sides to the argument.
- Buying links from high traffic sites to boost rankings.
- Buying links from high traffic sites to boost visitor numbers.
- Buying links from high traffic sites for visibility and branding purposes.
- Buying links from anywhere you can to get both the above.
The most important of these I would suggest would be number 3. Buying links to increase visitors or to just boost rankings is counterproductive. Sure you will increase your rankings and visitor numbers in the short term but eventually those visitors will likely not return. You need to improve your branding so people know who you are and want to come back.
Number 4 on the list is what is likely to get you penalised, not because you have bought a large amount of links, but more because you have bought them in known spam networks.
Clever buying of links is important for SEO. Its part of the big picture, SEO has never been just about getting visitors to your site, its about prolonging the relationship you have with visitors or clients for long term gains instead of short term wins.