Keeping MacBook Pro on Sleep Mode for days
This is pretty close to my typical MacBook Air usage. Luckily, it seems that we're on track:


  For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Apple does not recommend leaving your portable plugged in all the time. An ideal use would be a commuter who uses her notebook on the train, then plugs it in at the office to charge. This keeps the battery juices flowing.


See Apple's page on laptop batteries for lots more information: apple.com

Keep in mind that MacBook batteries are estimated to live through around 1000 charge-discharge cycles before their max capacity drops to 80% (same source). Try to approximate the ideal scenario Apple describes, and avoid running the battery to near-zero between every charge.