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
26. 5.31 homunculus
27. 5.31 Pope Guilty
28. 5.30 Sys Rq
29. 5.20 stavrosthewonderchicken
30. 5.14 mathowie
31. 5.05 Fuzzy Skinner
32. 5.01 Alvy Ampersand
33. 4.92 grouse
34. 4.89 loquacious
35. 4.81 OmieWise
36. 4.68 ThePinkSuperhero
37. 4.55 quonsar
38. 4.52 shmegegge
39. 4.48 Miko
40. 4.47 damn dirty ape
41. 4.46 Ethereal Bligh
42. 4.36 LobsterMitten
43. 4.33 terranova
44. 4.25 bardic
45. 4.23 jessamyn
46. 4.21 amyms
47. 4.20 Abiezer
48. 4.20 Civil_Disobedient
49. 4.17 Brandon Blatcher
50. 4.15 orthogonality
51. 4.14 y2karl
52. 4.13 matteo
53. 4.06 rtha
54. 4.05 odinsdream
55. 3.99 dhartung
56. 3.97 Pastabagel
57. 3.93 mr_crash_davis
58. 3.91 ikkyu2
59. 3.83 pyramid termite
60. 3.82 tkchrist
61. 3.81 PhoBWanKenobi
62. 3.67 Dave Faris
63. 3.66 ROU_Xenophobe
64. 3.62 Kirth Gerson
65. 3.60 It's Raining Florence Henderson
66. 3.47 Dizzy
67. 3.46 kindall
68. 3.33 goodnewsfortheinsane
69. 3.32 mediareport
70. 3.31 burnmp3s
71. 3.31 dersins
72. 3.29 quin
73. 3.29 Pollomacho
74. 3.18 Mitheral
75. 3.17 troutfishing
76. 3.14 Eideteker
77. 3.14 scarabic
78. 3.12 davy
79. 3.04 desuetude
80. 3.00 Chuckles
81. 2.99 ParisParamus
82. 2.96 Faint of Butt
83. 2.93 psmealey
84. 2.92 fenriq
85. 2.92 fandango_matt
86. 2.91 Afroblanco
87. 2.88 salvia
88. 2.88 dobbs
89. 2.87 konolia
90. 2.85 CitrusFreak12
91. 2.84 maxwelton
92. 2.82 dios
93. 2.82 The Deej
94. 2.80 The World Famous
95. 2.75 Balisong
96. 2.69 loiseau
97. 2.68 paulsc
98. 2.68 Plutor
99. 2.64 Mr. President Dr. Steve Elvis America
100. 2.62 XQUZYPHYR

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
26. 220 baylink
27. 206 caddis
28. 203 tellurian
29. 202 anastasiav
30. 201 troutfishing
31. 200 mediareport
32. 198 blahblahblah
33. 194 Pretty_Generic
34. 191 amyms
35. 188 Gyan
36. 187 goodnewsfortheinsane
37. 176 loquacious
38. 176 riffola
39. 173 nthdegx
40. 171 dobbs
41. 170 fenriq
42. 169 specialk420
43. 167 delmoi
44. 165 tranquileye
45. 163 ericb
46. 159 brownpau
47. 159 plinth
48. 159 moonbird
49. 158 psmealey
50. 150 Wolfdog
51. 149 insomnia_lj
52. 148 monju_bosatsu
53. 143 orthogonality
54. 142 Artw
55. 139 Blazecock Pileon
56. 138 kliuless
57. 137 WolfDaddy
58. 136 ZachsMind
59. 131 spock
60. 128 dhruva
61. 126 Effigy2000
62. 124 Voyageman
63. 123 grabbingsand
64. 123 adrober
65. 119 lagado
66. 118 tiaka
67. 117 OmieWise
68. 117 fandango_matt
69. 116 rschram
70. 115 ColdChef
71. 113 signal
72. 112 carter
73. 112 KevinSkomsvold
74. 111 holgate
75. 110 aaron
76. 110 Mwongozi
77. 109 tamim
78. 109 Brilliantcrank
79. 108 taz
80. 108 Ufez Jones
81. 106 klangklangston
82. 105 quonsar
83. 105 grumblebee
84. 104 jonp72
85. 103 dersins
86. 103 nofundy
87. 103 hadjiboy
88. 101 gman
89. 100 jonmc
90. 100 tdecius
91. 100 me3dia
92. 100 Irontom
93. 98 peacay
94. 97 magullo
95. 96 not_on_display
96. 95 Astro Zombie
97. 94 Miko
98. 92 Brandon Blatcher
99. 90 the fire you left me
100. 89 joeclark

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
26. 5710 clevershark
27. 5705 klangklangston
28. 5702 quin
29. 5672 UbuRoivas
30. 5610 fenriq
31. 5608 Civil_Disobedient
32. 5537 bardic
33. 5463 rushmc
34. 5376 tkchrist
35. 5118 kindall
36. 5112 Pollomacho
37. 5095 skallas
38. 5051 loquacious
39. 5040 bugbread
40. 5034 Postroad
41. 4994 stbalbach
42. 4970 ROU_Xenophobe
43. 4948 mathowie
44. 4916 XQUZYPHYR
45. 4812 kirkaracha
46. 4720 mediareport
47. 4658 ColdChef
48. 4637 cortex
49. 4544 wendell
50. 4239 soyjoy
51. 4216 pracowity
52. 4189 KirkJobSluder
53. 4173 lodurr
54. 4089 sonofsamiam
55. 4075 nofundy
56. 3858 mr_roboto
57. 3840 srboisvert
58. 3760 shmegegge
59. 3701 mrgrimm
60. 3649 jpoulos
61. 3638 thomcatspike
62. 3622 OmieWise
63. 3542 MiguelCardoso
64. 3510 raysmj
65. 3478 Ethereal Bligh
66. 3458 Mister_A
67. 3456 Balisong
68. 3427 owillis
69. 3384 Faint of Butt
70. 3345 Pope Guilty
71. 3324 holgate
72. 3256 Pastabagel
73. 3244 madamjujujive
74. 3229 orthogonality
75. 3220 davy
76. 3167 Mitheral
77. 3138 George_Spiggott
78. 3129 jfuller
79. 3115 Burhanistan
80. 3109 jonson
81. 3076 Mayor Curley
82. 3046 dobbs
83. 3021 Miko
84. 3014 Space Coyote
85. 2955 dejah420
86. 2934 odinsdream
87. 2910 dios
88. 2877 konolia
89. 2867 Heywood Mogroot
90. 2865 Alvy Ampersand
91. 2836 yhbc
92. 2813 alumshubby
93. 2789 brundlefly
94. 2773 Pretty_Generic
95. 2758 davidmsc
96. 2719 dreamsign
97. 2701 rcade
98. 2625 fandango_matt
99. 2614 aaron
100. 2612 PinkStainlessTail

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.