You need to also set the shadow opacity, it defaults to 0 and you won't see anything if you don't explicitly set it.
CALayer Reference
cell.layer.shadowOffset = CGSizeMake(1, 0);
cell.layer.shadowColor = [[UIColor blackColor] CGColor];
cell.layer.shadowRadius = 5;
cell.layer.shadowOpacity = .25;
Also note, that if you don't set the shadow path you will have terrible performance on the iPhone/iPad. Use something like the following code to set a shadow path, it removes the need to blur the layers underneath your tableviewcell's to create a "high quality" shadow.
CGRect shadowFrame = cell.layer.bounds;
CGPathRef shadowPath = [UIBezierPath bezierPathWithRect:shadowFrame].CGPath;
cell.layer.shadowPath = shadowPath;
Watch video 425 (also 424 and 426) to learn more about shadows from the WWDC 2010 Videos available here: WWDC 2010 Session Videos