What Google may consider low-quality links:

Here is the list that Google mey consider low quality links

• Links from sites with too many outgoing links
• Links from low-quality blog networks
• Links from sites with too many consecutive links (like sponsored links)
• Too high a number of sitewide links
• Too many links from sites with low Google PageRank
• Too many links from sites with related IP addresses
• The use of a certain keyword too many times in a link anchor text
• Links from sites with a subject that is irrelevant to your own site
• Links from link exchange-type pages
• Links from low-quality directories
• Links from footers
• Links from blog and forum comments

For backlink reviews, try SEOMoz’s OpenSiteExplorer.com and Majestic SEO