Thanks for replies! I'll try to reinstall (just to be sure) Opensolaris to flash drive and add debugging options to GRUB's boot command when I'm home, and look what happens then.
Concerning installation to USB flash drive - yes, it went smoothly and nothing wrong was seen in the installation logs. I just had to add proper lines to main system's /boot/grub/menu.lst to chainload GRUB's instance which resides on the flash drive. This message posted from opensolaris.org
