1. 12.33 Joe Beese
2. 10.96 DU
3. 10.63 amberglow
4. 9.77 ericb
5. 8.89 Marisa Stole the Precious Thing
6. 8.79 flapjax at midnite
7. 8.73 delmoi
8. 8.45 klangklangston
9. 8.18 Blazecock Pileon
10. 8.10 The Whelk
11. 8.06 Artw
12. 7.74 languagehat
13. 7.31 Astro Zombie
14. 7.17 Burhanistan
15. 7.02 jonmc
16. 6.89 cortex
17. 6.54 five fresh fish
18. 6.27 Ambrosia Voyeur
19. 6.02 Mister_A
20. 6.00 caddis
21. 5.72 Smedleyman
22. 5.68 UbuRoivas
23. 5.61 desjardins
24. 5.45 bugbread
25. 5.41 not_on_display

1. 1135 mathowie
2. 924 homunculus
3. 602 jonson
4. 561 Postroad
5. 481 y2karl
6. 460 MiguelCardoso
7. 442 stbalbach
8. 381 Steven Den Beste
9. 381 madamjujujive
10. 379 crunchland
11. 346 owillis
12. 321 amberglow
13. 319 plep
14. 306 skallas
15. 300 hama7
16. 290 kirkaracha
17. 274 srboisvert
18. 270 XQUZYPHYR
19. 264 matteo
20. 260 wendell
21. 257 Kattullus
22. 257 semmi
23. 254 flapjax at midnite
24. 236 feelinglistless
25. 227 mr_crash_davis

1. 19236 amberglow
2. 17854 delmoi
3. 16212 jonmc
4. 12531 homunculus
5. 12202 ericb
6. 11643 five fresh fish
7. 10250 dhartung
8. 9014 Artw
9. 8981 quonsar
10. 8719 languagehat
11. 8660 Smedleyman
12. 7532 y2karl
13. 7462 DU
14. 7458 matteo
15. 7194 ZachsMind
16. 7041 caddis
17. 6964 ParisParamus
18. 6838 stavrosthewonderchicken
19. 6666 mr_crash_davis
20. 6566 pyramid termite
21. 6385 troutfishing
22. 6381 flapjax at midnite
23. 6056 Astro Zombie
24. 5851 psmealey
25. 5792 Blazecock Pileon

Excellent question. It is simply the sum of all the times a user has posted on Metafilter (comments or threads on the blue, gray and green) divided by the number of days they have been a member.

Tamim's user profile discusses the idea and while reading this discussion I saw moz's reference to tamim's user page. After reading that and seeing tamim's suggestion, I wrote a quick script to do it. If you see any problems please let me know.