ftwb05 - 7:30 pm on Nov 14, 2007 (gmt 0)
If you're building links manually, with e-mail requests, responses, etc, unless you have a team of people helping you, you're unlikely to reach the level of link building that would cause problems.
The bad boys create thousands and thousands of links very quickly, they'll get caught out, or maybe not ;-)!
For a link to be worth anything it should be from a related page / site with natural anchor text, or so the general consensus goes.
Try and find a reputable links broker that specializes in your field, and they'll send you plenty of requests for links, usually from OK sites, but they tend to be "growers" that is new sites. This sort of link will grow in value over time.
You need lots of patience.