Consider Link Strength

[eagle09]

1. Keywords in anchor text (individually)
2. Keywords in anchor text (exact phrase match)
3. Keywords anchor in text (order of keywords if not exact match)
4. Length of anchor text (in words, not characters)
5. Placement on page
6. Proximity of non-link text
7. Proximity of link text
8. Density of surrounding non-link text
9. Density of surrounding link text
10. Relevancy of anchor text (to the page it's on)
11. Relevancy of anchor text (to the landing page)
12. Relevancy of anchor text (to the rest of the site)
13. Number of links on page using same anchor text (exact match)
14. Number of links on page using similar anchor text
15. Repeat 13 and 14 for entire site
16. PageRank of page link is on
17. Depth of page (subdirectory-wise) that the link points to (in relation to the page it is on)

[surreypcsupport]

1. Keywords in anchor text (individually)
2. Keywords in anchor text (exact phrase match)
3. Keywords anchor in text (order of keywords if not exact match)
4. Length of anchor text (in words, not characters)
5. Placement on page
6. Proximity of non-link text
7. Proximity of link text
8. Density of surrounding non-link text
9. Density of surrounding link text
10. Relevancy of anchor text (to the page it's on)
11. Relevancy of anchor text (to the landing page)
12. Relevancy of anchor text (to the rest of the site)
13. Number of links on page using same anchor text (exact match)
14. Number of links on page using similar anchor text
15. Repeat 13 and 14 for entire site
16. PageRank of page link is on
17. Depth of page (subdirectory-wise) that the link points to (in relation to the page it is on)

Nice list. You are right to highlight that only links with certain characteristics are of value to the optimiser.