Now for a quick runthrough of every version.
Windows 7 Starter is for emerging markets mostly, but also for some netbooks as an option. It's pretty gimpy, and only runs three apps at a time, though it'll have the new taskbar, Device Stage and jump list. Since Home Premium (and even the Ultimate beta) runs pretty well on netbooks, most of them are probably going to stick with that, so don't worry too much about it.
Windows 7 Home Basic is for developing markets only.
Windows 7 Home Premium is the standard consumer offering of the OS with Aero Peek, Media Center and all the other cool features we've been talking about, and what most people will be running, whether they're on a desktop or a netbook. It's better at media than Vista Home Premium, since it ships with DVD playback and codecs like DivX out of the box. In case you're wondering why Microsoft kept the "Premium" tack-on despite the extinction of Basic—it's because in market testing, Vista users thought they were getting downgraded, going from Vista Home Premium to Windows 7 Home.
Windows 7 Professional has everything that Home Premium does, but with business and "enthusiast" features like file encryption, location-aware printing and advanced backup.
Windows 7 Enterprise is for businesses buying OS licenses in bulk, so you probably won't have to worry about it (unless you're paid to). It's got everything Professional does, but with a few additions like BitLocker full-disk encryption and direct access capability, so you don't have go through a VPN for remote access.
Windows 7 Ultimate is, as you might have guessed, the ultimate version of Windows. Unlike Vista, where it was the combo of Home and Business with a couple added features, this time, it's like the end user version of Enterprise—in other words, the Enterprise version that regular people can buy. It has BitLocker, notably, and a few other advanced features. It seems like visibility of this will be low, outside of a few "special promotions" from vendors occasionally, to minimize confusion.