1680x1050 worth it?

Eww. Math. =P

You guys should just simplify things.

Reading fonts won't really matter. First of all, you can easily adjust the font size in Windows. Two, there's such a thing called ClearFont or ClearType (can't remember which one is correct) and as it's called, it makes text clear and sharp for easier reading. Three, looking at different resolutions aside from the native resolution of the monitor may differ from person to person because it's highly subjective.

Aside from the resolution, also consider the response time of the monitor. If you're planning on gaming, it's important because slow response time will cause tearing. It's going to cause a lot of strain on the eyes if you're exposed to this a lot. And for games that require fast reflexes, you need better monitor response so the screen doesn't blur a lot when a lot of action occurs.

Playing at non-native resolutions will only slightly decrease picture quality. It's actually neglible, but then again, it's subjective. I don't mind playing at 1280x960 or 1280x1024 since playing at my laptop's native resolution is just too much. More screen estate and resolution is always better for multimedia guys, especially Photoshoppers.

To make it really simple:
1) No need to worry about font because as aforementioned, it can easily be adjusted to suit your needs. Absolutely no problem with that.
2) Check the response time of the monitor. Get a monitor with at least 8 ms response time if you're planning on playing games, especially FPS and racing games.
3) Higher native resolution = usually better, especially for video and image editors/multimedia fanatics. Not to mention high resolution, more bragging rights. XD 1920x1200 is overkill for 15.4". Don't bother with this resolution unless you really wanna brag. >_<
4) 1280x960 is absolutely fantastic for monitors with 1680x1050 resolution. Trust me. Just make sure you get the screen aspect ratio right and you're all set. XD

I hope I helped

~Phonse