My facebook user id is 4102153. If you signed up for facebook for the swarthmore network, yours should be 41xxxxx as well. [1] I believe ids were handed out sequentially back then, which would make me the 2153rd user in the swarthmore network. Facebook doesn't do this anymore, so newer users have ids that don't tell you much (anything?), but the old table, as far as I can tell [2], is:

school	prefix(es)
harvard	00
columbia	01
stanford	02
yale	03
cornell	04
dartmouth	05
upenn	06
mit	07
nyu	08
bu	09
brown	10
princeton	11
tufts	17
northeastern	18
university of illinois	19
university of michigan	22
uchicago	29
williams	39
amherst	40
swarthmore	41
wesleyan	42
oberlin	43
middlebury	44
hamilton	45
bowdoin	46
cmu	48
university of maine	58
smith	59
keene state college	69
haverford	75
rutgers	88
umass amherst	91
reed	97
brandeis	98
bryn mawr	103
mount holyoke	104
umiami	106
georgia tech	128
emmerson	130
pomona	133
mcgill	136
perdue	137
connecticut college	141
university of rhode island	143
bates	146
colby	154
lafayette	166
carleton	191
macalester	194
lesley	198
clark	215
hampshire	227

You can see how facebook started out with harvard, and then spread to other schools close to harvard in terms of social networks.

About half of my friends signed up during the period when facebook was assigning ids like this.

I can also see how much of an early adopter people are. For example, mark handler (4100006) was #6 at swarthmore. The median among my friends is #2530, which means I wouldn't have to feel so bad about being 2153rd, except that swarthmore is on the small side and many of these people were signing up at much larger schools.

[1] One way to find out your facebook id is to look here while signed in. Another is to comment here (via facebook) and I can tell you.

[2] From looking at where my friends sorted by id went to school. Look at the api and click the link it has for "Friends"