Okay, I have been challenged to provide references thanks to you, Barbara
Wilson-Clay (and thanks for the compliment).  I decided that I would do a
quick medline search rather than search thru all my old school stuff.
So... the literature on this topic is mixed with some studies saying there
is no relation between fibrocystic breasts and some proporting a link.
Both of the studies supporting a link between caffeine intake and symptoms
are a bit older but the references and abstracts are here FYI. The second
one is probably more relevant to our discussion as what it really
addresses is caffeine elimination and subsequent reduction of breast pain.

 Like Barbara, I really do not like giving women a list of "thou shalt
nots"  with breastfeeding, and try to refrain from ever doing so. As I
mentioned in my earlier post, though, most of the women whom I see having
problems (usually tenderness) with cyclic breast pain are in their late
30's to 40's.  In my experience and the reported experiences of women I
have worked with, cyclic breast pain has not generally been problematic
during breastfeeding, but if it were, suggesting a trial of elimination of
caffeine to see if symptoms improved would seem a reasonable first step,
after ascertaining that it was cyclic breast pain that was really being
dealt with, not pain from some other cause.

References:

Boyle, CA, Berkowitz, GS, LiVolsi, VA, Ort, S, Merino, MJ, White, C, &
Kelsey, JL (1984). Caffeine consumption and fibrocystic breast disease: a
case controlled epidemiologic study. J Natl Cancer Inst, 72(5), 1015-9.

In a hospital based case controle study that included 634 women with
fibrocystic breast disease and 1,066 comparison women in Connecticut, the
occurrence of fibrocystic breast disease was positively associated with
average daily consumption of caffeine.  Women who consumed 31 -250 mg
caffeine/day had a 1.5 fold increase in the odds of disease whereas women
who drank over 500 mg/day had a 2.3 fold increase in the odds.

Russel, LC (1989). Caffeine restriction as initial treatment for breast
pain. Nurse Practitioner, 14(2), p. 37-8

The effects of methylxanthines (caffeine, theophylline and theobromine) on
the symptoms associated with fibrocystic breast disease were studied in
147 patients. Disease was documented by mammography, physical examination
and clinical symptoms. Only those individuals with breast pain (n=138)
were included in the study. Questionaires were presented and explained to
all patients by the same nurse examiner. Patients reported their degree of
caffeine consumption as either light (two cups per day or less of caffeine
containing foods or beverages), moderate (more than two cups, less than
six cups per day), or hearvy (six cups per day or more of caffeine
containing products). They additionally reported breast pain as milk,
moderate, or severe. Past medical and family histories wer reported as
well as medication intake. All patients were counseled to abstain from or
reduce caffeine consumption and were given a list of commonly used
caffeine-containing products. The results at the end of one year indicated
that compliance was high with 113 patients reducing their caffeine intake
substantially, and of those, 69% reproting a decrease or absence of breast
pain.

Ione Sims, CNM, IBCLC