One thing to keep in mind about rate movements is the time frame. Rates are now at historic lows and seem likely to move higher over time. But over what period of time? Short term bond investments have maturities of 18 months or less. It is much less clear that rates will move up that quickly, and could conceivably decline. A balance between long and short term bond investments avoids placing heavy bets on the direction of rates in the near time horizon. At the same time, having a variety of maturities allows you to follow rates up as they rise, even if you are invested in long term instruments.

Depends where you think rates will go. My article here is about savings, but it describes a few strategies with bonds and also discusses the problem with guessing rate movements:

http://www.filife.com/stories/help-im-only-earning-1-on-my-savings