When Google releases their Chrome OS, my first prerequisite would be to work with my current files. What filesystems would it work with? (have read-write access). Would it support Windows partitions? (NTFS) and Unix partitions? (EXT/UFS). And lastly, which filesystem would it use natively and/or perform best with?
As it's going to be based on the Linux kernel, I think you would be pretty safe in assuming it will support the usual ext3 filesystem.
It's impossible to guess what Google are going to do, but if they want to make any progress with their 'OS' they will need to ensure a maximum level of interoperability with existing systems to make the changeover as easy as possible for new users.
It really depends on how easy Google wants to make for people to switch to their operating system.
If we look at when Microsoft introduced NT for the first time, it supported as much hardware and file systems as possible, and it continues to support both HFS, NTFS and FAT32 out of the box.
So if Google wants to build bridges to the ChromeOS, they should support HFS+, NTFS, FAT32 and ext3 that way it will ease transition and compatibility with other operating systems and maximise their chances of commercial success.
Given that it is going to be targeted at Netbooks I don't think that native Windows FS support will be that high on the agenda. NTFS support is mainly useful if you are dual-booting and want to be able to access the other OS.
I would expect ext3 (possibly 4) for the native partition as well as CIFS for network shares, FAT(16/32) for mounting USB devices and possibly a FUSE based cloud storage (GDrive has been rumoured for a long time but I'm still not convinced it is coming).
Given that it is a Linux Kernel many other filesystems are potentially available but many will probably be dropped to minimise the install size and boot time.