This study was just published this week.  I post mostly to
sci.life-extension, but thought this study may be of interest here.

BTW, the first nitrogen-stabilized and bioavailable resveratrol
product just became available to consumers last month.  The belief,
based on testing by scientists at Harvard University, is that
resveratrol readily oxidizes and loses potency.  The resveratrol used
for scientific experiments is manufactured and preserved in a nitrogen
environment to prevent oxidation.  However, with the exception of the
new resveratrol product which just became available, all other
resveratrol products available to consumers are not
nitrogen-stabilized.

Resveratrol can also be found in significant amounts (although not as
high as in a pill) in certain red wines.  However, after the bottle of
wine is opened, the resveratrol rapidly oxidizes and loses potency.
(Think of a sliced apple that turns brown after sitting for a short
time).

Oncol Rep. 2004 Feb;11(2):441-6.

Resveratrol inhibits cell proliferation and induces apoptosis of human
breast carcinoma MCF-7 cells.

Kim YA, Choi BT, Lee YT, Park DI, Rhee SH, Park KY, Choi YH.

Department of Oriental Medicine, Dongeui University and Research
Institute of Oriental Medicine, Busan 614-052, Korea.

Resveratrol, which is found in grapes and wine, has been reported to
have a variety of important pharmacological effects including
anti-inflammatory, anti-platelet, and anti-carcinogenetic properties.
In this study, using the human breast cancer cell line MCF-7, we have
analyzed a possible mechanism by which resveratrol could interfere
with cell cycle control and induce cell death. Resveratrol treatment
of MCF-7 cells resulted in a dose-dependent inhibition of the cell
growth and the cells accumulated at the S phase transition of the cell
cycle at low concentrations, but high concentrations do not induce S
phase accumulation. The anti-proliferative effects of resveratrol were
associated with a marked inhibition of cyclin D and cyclin-dependent
kinase (Cdk) 4 proteins, and induction of p53 and Cdk inhibitor
p21WAF1/CIP. Growth suppression by resveratrol was also due to
apoptosis, as seen by the appearance of a sub-G1 fraction and
chromatin condensation. In addition, the apoptotic process involves
activation of caspase-9, a decrease of Bcl-2 as well as Bcl-XL levels,
and an increase of Bax levels.

PMID: 14719081 [PubMed - in process]