I'm using the IE Webcontrols:

www.asp.net/.../Download.aspx?tabindex=0&tabid=1

I use a tabstrip linked with a multipage. What's nice about it is
it will keep everything in viewstate  for you, so you can flip
between tabs and keep the same information you filled out or
modified on that tab.

1. session  variables take up server memory. They can work, but
remember not to shove tons into session variables. Manage your
session well.

2. True, viewstate dies if not posting back  to the same page  (from
what I've experienced). I believe you can maintain viewstate across
different pages  though if you make sure it is enabled on every page
and every control. It should be...

3. That's the old way. If anything, use viewstate, then session,
then querystring. querystring  is good to directly pass  variables to
a specific page directly. It depends here. I don't know how much
data you're putting in the querystring. Look at Yahoo!. They put
tons of stuff in the querystring.