ext3cow FS?

[Scott R. Ehrlich]

I just found an article comparing Ubuntu Linux (7.04) to Vista, and one of 
the areas they compare is backups.   In that section they mention ext3cow, 
which was the first time I'd heard of it.

What are people's insights of ext3cow?   I haven't had to recompile a 
kernel in ages - it seems the default ones, for the most part, for Ubuntu 
and CentOS, anyway, are fully robust to handle whatever I throw at them.

So how does something like ext3cow for some kind of backup/restore fair?
What other similar tools do people use?   How about for systems that are 
actively in use that I may opt to insert this functionality, ideally 
without rebooting, but if needed, I would.

Thanks.

Scott