the digital in is specifically useful if you have an A/D...or want to dump data from an external digital recorder without a computer interface. It's probably sufficiently weird most people wouldn't need one tho.
In looking more closely at the new macbook, it appears it's also lost the optical input. There's now 1 port, a combined optical out, headphone out, analog in. It's possible you can also do digital in, but they don't talk about that on the specs page.
ah, the old "tie a steak around her neck and at least the dogs will play with her" trick.
If it takes a good car for her to be popular, she won't be popular.
Why not stick with what you have until there is a compelling upgrade? Don't buy a computer for future upgrades, it'll be cheaper to get that later. I personally always shoot for the midpoint of what's current, or a top of the line previous gen system.
Jeff, watch the credit card accounts you used with HD tracks. I read recently that there was some fraud that was believed to be tied to accounts used at HD Tracks, so they may have been compromised.