it's being done all the time with desktops, but laptops are still a bit more finicky, due to all the integrated hardware they have. I'd be interested to know as I plan on putting OS X on my DS3R when it's built to get some Mac experience (they're getting more and more popular. if I have any hopes of supporting Mac in the future, I need to know how to use it!) and thought if it's possible, maybe pop it on my laptop as well.
insanelymac.com leads to a forum and wiki where there should be plenty of compatibility information. If you need help with a specific issue drop by #OSx86 on irc.moofspeak.net.
There are large compatibility lists on the wiki.
We will be seeing the return of JaS soon as well, he "retired" a while ago after 10.4.8 If I recall but he decided to whip up a 10.5.2 image. :) The 10.5.2 Kaylway DVD is said to be really good though.
Also, I am pretty happy about how there have been recent developments in regards to the Attansic L1 or w/e the onboard ethernet this Asus P5K of mine has.
Unless I am mistaken the P35 Gigabyte boards generally have great compatibility.
With portables you _really_ have to pay attention to what hardware it has. For example, with GMA3100 you cannot get Quartz Extreme and Core Image but with GMAX3100 you can.
Just pay attention to the hardware and search the forums and wiki for people have tried it. If nobody has then see if it works and report back to the forum/wiki with your results. :P
Compatibility with hardware seems to be increasing as users keep writing and patching drivers for previously unsupported hardware but it is not "install and use on anything" yet.