Comparing Google's Picasa Web to Flickr
I have had a Flickr photo site for a long time and I plan on keeping both sites, at least for now. (I link to both Picasa Web and Flickr on my main web site).
I think that the web interface for managing photos is better for Flickr, but Picasa Web is also very easy to use and was only publicly released this week - I am sure that it will get even better. I requested a Picasa Web invitation early in the morning the day it was released and I received an invitation within a day. I don't know what the waiting time is now. Google may want only a relatively small number of test users to initially test the system.
It will be interesting to see if Picasa Web will be profitable by selling extra storage space and hard copy prints, or if they will add advertisements to the Picasa Web pages to generate revenue.