Update: I changed the code to:

CGSize constraintSize;constraintSize.width = 260.0f;constraintSize.height = MAXFLOAT;
NSString *theText = @"When in the Course of human events, it becomes 
necessary for one people to dissolve the political bands which have 
connected them with another, and to assume among the powers of the earth, 
the separate and equal station to which the Laws of Nature and of 
Nature's God entitle them, a decent respect to the opinions of mankind 
requires that they should declare the causes which impel them to the 
separation.";
CGSize theSize = [theText sizeWithFont:[UIFont systemFontOfSize:17.0f] constrainedToSize:constraintSize lineBreakMode:UILineBreakModeWordWrap];

theSize.height is 273. That seems more like it.

via stackoverflow.com

Turns out [NSString sizeWithFont: forWidth: wordWrap:] wasn't doing what I thought it was. Tip 'o the day!