Currently this is still a work in progress but so far I have all of the most important functionality working on this laptop (networking, X, kde, usb). I still haven't tried acpi states (suspend/hibernate).
Neither the wireless card nor the ethernet adapter worked when booting from the live cd (though I didn't try to hard to get them to work, so I decided to install from within a knoppix environment (on a side note, this is another great feature about gentoo, very well-documented installation and many options; and another side note, knoppix is a live saver too!). I did a stage1 installation following the gentoo manual and everything went perfect. I was using gcc 3.3 for the install so unfortunately I couldn't use architecture-specific optimizations (gcc3.4 has a march=pentium-m options I believe), but that's not a big deal.
It took quite a few tries to get X configured, here is my XF86Config, I think its pretty much right now, the only issue is with using an external monitor. When I start X with the external monitor connected, both screens will be on and I can't turn any of them off, and it uses the higher resolution setting. If I start/restart X with the external one not plugged in and later plug it in, I can turn off the laptop screen but it uses the lower resolution.
The biggest problem, I think, was getting the the ipw2100 (centrino wireless) stuff working.
First, I kept getting "unknown device" listings from lspci and I thought that was the problem. After reading some manpages, I realized that all i had to do was update-pciids and the correct names were there. However, this was not the solution to the problem. When i loaded the ipw2100 module, dmesg output would tell me that it was unable to allocate IRQ 7. This wasn't all that helpful, but after much research, I realized that the problem stemmed from IRQ 7 being typically required for parallel ports. At the time, I had parport built straight into the kernel (although I'm not quite sure why, oh well) So I changed it to a module, and after rebooting, everything went perfectly. All I had to do is modprobe ipw2100
and ifconfig immedieately showed me the new network connection.
The ethernet card works fine with the Tigeon 3 kernel drivers, though I never use it. Also, I haven't tried the modem either, but the Linuxant drivers should work (i've used them in the past with success).
I still have not been able to get any of the power management features working. It always gets to the screen that says its shutting everything down, but then it just freezes. Fortunately, the system boots up pretty quickly, and kde's session saving utility is really helpful.
Sound works perfectly using the ALSA drivers found in the kernel for intel. Sometimes I get errors saying that the sound card is used when using xmms from within kde, but its no big issue, maybe just configuration stuff.