26.22 Miles (26 miles 385 yards)
Record a/o Dec. 2008:
Men 2h03:59 - Haile Gebrselassie, Ethopia
  7 of the top 10 times were by Kenyans
Women: 2h15:25 - Paula Radcliffe, GB

Qualifying times for Boston Marathon (18-34 age bracket):
Men   3:10:59 (3 hours and 10 minutes) ( 7:17 min./mile)
Women 3:40:59 (3 hours and 40 minutes) 
An exception to the qualification requirement is awarded to 1,250 runners who
raise a pre-determined level of sponsorship for officially designated local charities.

Equivalent pace (av. mile times)
2:11   -  5    min/mi
3  hr  -  6:51 min:sec/mi
3.5 hr -  8    min/mi
4 hr   -  9:09 min/mi
4.5 hr - 10:18 min/mi
5 hr   - 11:26 min/mi

California International Marathon (CIM)
Coverage at KCRA Channel 3
CIM 2008 Results (fastest by division [age group])

Men					Women
Div	num	top	median	90%		num	top	median	90%
19UND	33	3:15	4:04			20	3:30	5:03
20-24	111	2:28	3:57	5:03		146	2:39	3:58	5:03
25-29	268	2:17	3:39	4:45		300	2:32	4:09	5:14
30-34	400	2:17	3:38	4:44		355	2:37	4:10	5:21
35-39	528	2:27	3:42	4:50		380	2:44	4:14	5:20
40-44	530	2:30	3:45	4:48		366	2:41	4:13	5:04
45-49	466	2:37	3:50	4:54		311	2:53	4:18	5:17
50-54	327	2:47	3:57	4:57		186	3:18	4:17	5:23
55-59	197	2:48	4:06	5:13		73	3:52	4:47	5:59
60-64	100	2:51	4:13	5:08		28	3:31	4:40	5:51
65-69	31	3:17	4:17	5:57		14	3:51	5:09	5:44
75-79	5	4:17	5:17	5:30
Total	3011	2:17	3:51			2185	2:32	4:16

90% - 90% of times were this or less.
Sample size was small with 14 women in the 65-69 group and 14 men in the 70-74 group.
Source: www.runcim.org/data/08Results.html

Some observations:
Women's times generally get better after those big birthdays, 40, 50 & 60.
Women peak earlier (20-24) than men (25-29) and drop off earlier (55-59) than men (70-74). This is a generalization, Paula Radcliffe set the worlds record at the age of 30 and Grete Waitz won her 9th New York marathon and Radcliffe her 3rd, both at the age of 35.

  Men 30-39 (a smoother distribution).
One sigma (standard deviation) is 45 min.
(I don't know how to calculate the upper limit for a gamma distribution [are race times gamma?] but it is something greater than 4:24)

American Marathon drought:
The days of the days of Salazar, Beardsley, and Rodgers are long gone. The last American to win the Boston Marathon was Grey Meyer in 1983. Americans are lagging behind rivals from many other countries, including Japan, Mexico, Australia and African nations like Kenya, Ethiopia and Tanzania.
Ryan Hall, with a 2:08:24 in his debut Marathon in 2007 and tenth in the Olympic marathon in Beijing, will run in 2009.

Links:
USA Track & Field (USATF)
www.MarathonGuide.com
Marathon at wikipedia Training:
MarathonTraining.com
www.MarathonRookie.com/
Marathon Training: RunnersWorld.com
Marathon-training.net