A bit late, but here's an update of the Time Machine exclusion list for Snow Leopard.Here's the full list of the excluded paths:

Contents Excluded

The contents of these paths are excluded, but the directories themselves are preserved as they are required for a successful restore. Remains the same as in Leopard.

/Volumes
/Network
/automount
/.vol
/tmp
/cores
/private/tmp
/private/Network
/private/tftpboot
/private/var/automount
/private/var/run
/private/var/tmp
/private/var/vm
/private/var/db/dhcpclient
/private/var/db/fseventsd
/Library/Caches
/Library/Logs
/System/Library/Caches
/System/Library/Extensions/Caches

These folders are excluded pre 10.5.something [Does anyone know when these came about?]

/private/var/log
/private/var/folders
/private/var/log/apache2
/private/var/log/cups
/private/var/log/fax
/private/var/log/ppp
/private/var/log/sa
/private/var/log/samba
/private/var/log/uucp
/private/var/spool

Paths Excluded

These directories and their contents are excluded completely. Remains the same as in Leopard.

/.Spotlight-V100
/.Trashes
/.fseventsd
/.hotfiles.btree
/Backups.backupdb
/Desktop DB
/Desktop DF
/Network/Servers
/Previous Systems
/Users/Shared/SC Info
/Users/Guest
/dev
/home
/net
/private/var/db/Spotlight
/private/var/db/Spotlight-V100

User Paths Excluded

These directories and their contents are excluded per-user. The path is relative to the user's home folder.

Library/Application Support/SyncServices/data.version
Library/Caches
Library/Logs
Library/Mail/Envelope Index
Library/Mail/AvailableFeeds
Library/Mirrors
Library/PubSub/Database
Library/PubSub/Downloads
Library/PubSub/Feeds
Library/Safari/Icons.db
Library/Safari/WebpageIcons.db
Library/Safari/HistoryIndex.sk

File Contents Excluded

These directories are not themselves excluded, but the files in them are. The directories will be recreated on restore. Remains the same as in Leopard.

/private/var/log
/private/var/spool/cups
/private/var/spool/fax
/private/var/spool/uucp