My lumber salesman just incorrectly had lumber dropped off at my jobsite.He was to wait on my call for the go ahead.The problem is because of the rain my foundation floor hasn't even been poured yet and the rain is still coming down I'm worried about my lumber being exposed to the rain for a long period of time.Should I be concerned?

No. Probably only the boards on the surface will be really wet, and they will dry out quickly with good weather. The strength will not be affected. The straightness of some pieces might be, but the framers will know how and where to use lumber that isn't straight, and they even have ways of straightening some of it.

KEEP IT TARPED AND BANDED UNTIL NEEDED. IF POSSIBLE GET STICKERS UNDER IT SO THE BOTTOM PIECES DON'T GET SATURATED AND MUDDY. ESPECIALLY KEEP OSB SHEATHING AS DRY AS POSSIBLE. FOR THE MOST PART , LUMBER CAN BE EXPOSED TO WEATHER FOR 3-6 MONTHS UNTARPED, ALMOST FOREVER IF TARPED. JUST MAKE SURE IT'S REALLY DRY BEFORE YOU SHEETROCK OR YOU'LL HAVE NAIL POPS LATER.DRY WARM WEATHER OR YOUR FURNACE WILL DO THE TRICK

What about the "swimming pools" created when rain collects between the bottom wall plates and on top of the OSB? I question whether the OSB will be able to ever dry out before the interior flooring is put down?

Usually OSB (oriented strand board) is made with a coating on one side which will withstand the effects of water for the period of time a home is under construction. If it was installed with the correct side up, it should cause no problems. Nevertheless, a good builder will sweep away any water which accumulates on the subfloor, and not allow it to stand.

Of course it is inevitable that it rains on your house while in the framing process, but like Richard said, the OSB can withstand this rain, as long as it's dried out before you permanantly cover it then you will be fine, and if your builder or flooring installer attempts to install flooring on a wet floor, then you should immediately escort him off the property and not allow him back.

When my home was being constructed (rough framine), it rained almost every day - all summer long. I had to drill holes in the OSB to drain the dams. Then, after the monsoon season was over, the OSB dried out. Some of the edges swelled. So, before installing any other flooring, I used a rough floor sander and leveled everything. This worked well. One caution. Go over (under) every inch of subfloor on floor joists. Pull every nail that misses or partially misses a floor joist, and, replace with 3-inch drywall screws - to eliminate future squeeks.