Hi,
I've got a Sony Vaio VGN-SZ1VP (dmidecode[1] and lspci[2]).
Using default kernel (linux-image-2.6.15-27-686) of Ubuntu
Dapper I've got /proc/acpi/sony/brightness and it works well
(yes, Ubuntu drivers/char/sonypi.c is patched).
With any other newer vanilla kernel, 2.6.15/16/17/18, /proc/acpi/sony
doesn't appear, and it's impossibile to set brigthness, of
course. Same thing with Ubuntu kernel package
(linux-image-2.6.17-9-386).
I tried to port Ubuntu sonypi.c patches to 2.6.18, but it doesn't
work (I mean, it compiles clean, it "modprobes"[3] clean, but no
/proc/acpi/sony/ directory).