If the yeild curve flattened the book value would rise. They can't both happen simultaneously because they are inverses of the treasury market (high price means low yeild, low price means high yeild, to reflect the variable risk.)
As such, with every quarterly report there will always be some good news and some bad news... it's a balancing act. Q4 will likely be a lower book value than Q3 with higher profitability if the Q4 treasuries give any indication. Likewise, Q1'13 will be higher book value on falling yeild spreads with falling profitability, and is likely to be more profitable than Q3 but less profitable than Q4.
Add to this the company buys themselves in share buybacks below book, and sells themselves in SPOs if it gets too high and you may see moves, but you'll generally see more stability than in the greater market.
Spreads are in the high 160bps range.
Remember: know what you own. By this rule you will have more confidence when the market moves against you by some amount. If you don't know what you own, don't buy.