How to find out the UID of a given file/folder?
I'd personally recommend using a terminal emulator or adb shell and then using the ls command. You can get the UID's listed by name if you use the -l flag and listed by number with the -n flag. Note that in the /data directory you'll need root permission in order to index the files/directories, so ls will fail with a normal user:

root@android:/data # ls -l
drwxrwxr-x system   system            2012-08-27 14:29 anr
drwxrwx--x system   system            2012-08-29 17:46 app
drwx------ root     root              2012-08-27 00:54 app-asec
drwxrwx--x system   system            2012-08-27 00:54 app-private
drwx------ system   system            2012-08-27 00:55 backup
drwxrwx--x system   system            2012-08-29 17:46 dalvik-cache
drwxrwx--x system   system            2012-08-29 17:34 data
drwxr-x--- root     log               2012-08-27 00:54 dontpanic
drwxrwx--- drm      drm               2012-08-27 00:55 drm
drwxrwx--- gps      system            2012-08-27 10:29 gps
drwxr-x--x system   system            2012-08-27 00:54 lightsensor
drwxr-x--x root     root              2012-08-27 00:54 local
drwxrwx--- root     root              1969-12-31 19:00 lost+found
drwxrwx--- media_rw media_rw          2012-08-27 14:10 media
drwxrwx--t system   misc              2012-08-27 00:54 misc
drwx------ root     root              2012-08-27 10:30 property
drwxrwx--x system   system            2012-08-27 00:54 resource-cache
drwxr-x--x system   system            2012-08-27 00:54 sensors
drwxr-x--- root     shell             2012-08-27 00:54 ssh
drwxrwxr-x system   system            2012-08-30 11:05 system
drwxr-xr-x root     root              2012-08-27 00:55 tf
drwx--x--x system   system            2012-08-27 00:54 user

root@android:/data # ls -n
drwxrwxr-x 1000     1000              2012-08-27 14:29 anr
drwxrwx--x 1000     1000              2012-08-29 17:46 app
drwx------ 0        0                 2012-08-27 00:54 app-asec
drwxrwx--x 1000     1000              2012-08-27 00:54 app-private
drwx------ 1000     1000              2012-08-27 00:55 backup
drwxrwx--x 1000     1000              2012-08-29 17:46 dalvik-cache
drwxrwx--x 1000     1000              2012-08-29 17:34 data
drwxr-x--- 0        1007              2012-08-27 00:54 dontpanic
drwxrwx--- 1019     1019              2012-08-27 00:55 drm
drwxrwx--- 1021     1000              2012-08-27 10:29 gps
drwxr-x--x 1000     1000              2012-08-27 00:54 lightsensor
drwxr-x--x 0        0                 2012-08-27 00:54 local
drwxrwx--- 0        0                 1969-12-31 19:00 lost+found
drwxrwx--- 1023     1023              2012-08-27 14:10 media
drwxrwx--t 1000     9998              2012-08-27 00:54 misc
drwx------ 0        0                 2012-08-27 10:30 property
drwxrwx--x 1000     1000              2012-08-27 00:54 resource-cache
drwxr-x--x 1000     1000              2012-08-27 00:54 sensors
drwxr-x--- 0        2000              2012-08-27 00:54 ssh
drwxrwxr-x 1000     1000              2012-08-30 11:05 system
drwxr-xr-x 0        0                 2012-08-27 00:55 tf
drwx--x--x 1000     1000              2012-08-27 00:54 user
root@android:/data #