Keep in mind that, if you're looking at the MacBook with DVD writer, you can get a Vista PC with a dedicated GPU and possibly even a blu-ray drive.
Many PCs (at least from HP) under $1,000 can be had with dedicated GPUs and similar real world battery life.
Even if you don't plan on playing games, dedicated GPUs make a world of difference when it comes to video playback quality. It's not even a contest. It's complete night and day.
I have an HP with a GeForce 8400M GS. Not only does video of all kinds (DVD, H.264, etc) look 100x better on the HP, but the CPU use is dramatically lower. 720p H.264 video on the MacBook can eat as much as 60% of one core (C2D 2.16GHz). But that same video on my HP (C2D 2GHz, Santa Rosa, GeForce 8400M GS) will peak at 7% of one core and go as low as 2%. Not only that, but the GeForce will do deblocking, proper color correction, proper upscaling, all of that neat stuff. Plus the MacBook's fans kick into high gear and it sounds like I have a small jet engine on my desk.
The HP can play blu-ray movies at lower CPU use than the MacBook playing standard DVDs. Plus the HP has an HDMI output thats HDCP certified so I can hook it up to my HDTV and watch blu-ray movies on it.
Like I said above, DVDs also look 100x better on the HP. The GeForce (even with Vista Home Premium's built-in decoder) will do practically ALL of the video work, from the deinterlacing to color correction to deblocking (getting rid of compression artifacting) and proper upscaling to any resolution. CPU use for DVD playback on the HP hovers around 2-5% for one core. On the MacBook it goes between 25-40% of one core. Plus DVD Player in OS X doesn't even have advanced audio features, such as the ability to decode the LFE channel (subwoofer) and send it out to speakers or headphones. All it has is a joke of an equalizer.
If video quality is a concern, stay away from the MacBook. The only way to get decent video out of Apple products is to go with something that has a dedicated GPU and install Windows on it. Same goes for movie sound quality. Explosions and anything requiring deep bass falls flat, literally, on DVD Player because of the lack of LFE decoding.