Because of the nice format of the iPad, and the quality of the screen, it is very confortable to watch pictures and your favorites photo albums with Picasa.
Some apps are even able to cache the photos in the internal memory, so you don't even need a connection to watch or show the pictures to your friends.

here is my selection of the best apps so far :

iPics for iPad 1.3+ is including a part of our project PhotoLikr ( you can rate by sliding up and down on any picture in full view to rate it and update your vote to our database )

My favorite is Web Albums for iPad by By Scott Sykora, available in the appstore for 3$

the publisher of ipicasso is providing a Picasa solution but also iPad version to access
or the publisher web site