Running in a marathon in the rain...any advice?

Weather forecast for Napa Valley Marathon, to be run on Sunday, is (as of this writing) 70 percent chance of rain with 6-8 mph southerly wind (which would be a headwind).  I've only run 3 marathons, none of which entailed running in rain.  Of course I've run in the rain a million times but never this far.  So does anyone have any advice I can steal?

I went to one of the many ubiquitous bike shops in Davis, CA (B&L) today and asked what cyclists do in the rain (our local Fleet Feet had no plausible jackets of any sort) and the very helpful clerk alerted me to the O2 rain jacket.  It seems like it is breathable and waterproof so I decided to get it (relatively cheap [$36] as far as gear goes).

             ...I worry though because I overheat pretty quickly.  I probably will only wear it if it looks like sustained rain (I also am loathe to throw gear by the side of the road in races as a: it's pollution and b: I PAID for that sh*t).  

So if anyone who happens to see this have any thoughts on running a marathon in the rain, I'd love to hear them.

Out.

B.

PS: I'm aiming to run around 3:16 (7:30 pace).