As of today, $999 will get you a MacBook with faster RAM (2x1GB SO-DIMM of 1066MHz DDR3 SDRAM, up from DDR2), a slightly faster processor (2.26GHz, up from 2.13Ghz), and a significantly larger hard drive (250GB, up from 160GB).
But those technical specs are just the beginning. There's a new built-in battery which Apple claims will take 7 hours per charge. This follows the trend of having batteries integrated instead of removable, which Apple has said allows them to make the laptops smaller and lighter. The battery is rated for "up to" 1,000 charges.
The MacBook also now has the glass Multi-Touch trackpad, previously seen on the MacBook Air and Pro models, the LED-backlit display. It is still "rugged polycarbonate" (marketing speak for "plastic") but now a unibody construction, like the Air and Pro models, except they use aluminum enclosures.
The outer shell may be the most notable difference between the MacBook and MacBook Pro models now. For $999, it's no longer an underpowered little sibling to the MacBook Pro line; it is a very respectable portable Mac. Students can save $50 using the education pricing.
If you're looking for an even lower price, there are a few refurbished MacBook models currently available for as low as $849, but with the new features available in today's model, I'd be tempted to spend the extra $150.