The HP ProBook 4430s is the first 14-inch laptop that I have ever recommended for Mac OS X (all of my other picks have been 15.6-inch or 17-inch). The specifications of the Probook 4430s are most directly comparable to the specifications of the 13-inch Macbook Pro. In fact, in most aspects, the 4430s and the Macbook Pro are essentially equal; both laptops use Intel's 2nd-generation Core i3 or Core i5 processors, and have very similar screen resolutions. Of course, the $600 ProBook only costs half as much the $1200 Macbook Pro. However, this low price comes with its own costs: ProBooks usually only get about 3 hours of battery life on Mac OS X, while the Macbook Pro tops off at nearly 7 hours.
In terms of Hackintosh ability, the 4430s lives up to the Hackintosh-friendly reputation of the HP ProBook line. Nearly everything works with Mac OS X: WiFi, ethernet, graphics, audio, trackpad, etc. Most of these features will actually work immediately after installing Mac OS X, without the need for any additional kexts or drivers. The few features that don't work out of the box can be activated with only a minimal amount of effort.
But as always, you'll still encounter a few problems with running Mac OS X on a ProBook. The VGA port is unreliable, since real Macs don't have VGA ports. Bluetooth doesn't work after waking up from sleep or a soft restart (you have to power off the ProBook completely when restarting it). Additionally, the external microphone doesn't work, which is a common problem with just about every Hackintosh notebook.
The ProBook 4430s isn't as popular as its big brother, the ProBook 4530s, so there is much less of a support community backing the 4430s. You won't find too many guides or help threads on the internet about the 4430s, but most of the time, the Hackintoshing guides for the 4530s will work without any trouble.
Resources: Snow Leopard install guide | Lion install guide