I've just noticed new article on Open Solaris site about Solaris for x86 notebooks. It's a nice overview of current status.
I have Solaris dual-booted with Windows on my current (and previous) laptop for quite some time - over 3 years now. I know some other people who do have Solaris on their laptops too. I agree with the article that installation is quite easy, there're some problems with drivers - although it's getting better every month. Few months ago I had to manually tweak Xorg configuration to get 1400x1050 - with latest Solaris Express it works out of the box. There's 1400x1050 background for login screen (such a small thing but makes feel it better). Then there's GRUB for some time (starting with b14) - so booting Solaris/Windows is more user friendly and is much faster now (due to new boot architecture that GRUB is part of). Then there're being added such small features like virtual mouse (works great!) which let's you to use touchpad and usb/ps2 mouse simultaneously, nforce chipset support, nvidia divers, battery support, and so on. One of a common problems is NIC support - I use sfe driver thanks to Masayuki Murayama - you can find more drivers there for common ethernet cards. Some manufactures like Broadcom provide their own drivers (although with Solaris comes bge driver which covers quite a lot of Broadcom NICs - sometimes it's just a metter of addind new id). USB pendrives and disk drivers - work too. WiFi from Sun is coming, and so on.
While Solaris on x86 notebooks is not perfect, it's gettint better literally month by month (thanks to Open Solaris and SX) and it works really good for a lot of people.