Here are some resources courtesy of a quick Google search:

General design approach:
http://forums.asp.net/t/1223582.aspx

A nice summary of viewstate:
http://aspalliance.com/articleViewer.aspx?aId=135&pId=

A more in-depth article on viewstate:
http://aspnetresources.com/articles/ViewState.aspx

Backgrounder on viewstate versus session:
http://forums.asp.net/p/1147538/1865335.aspx#1865335

Comprehensive reference on Understanding ASP.NET View State
http://msdn2.microsoft.com/en-us/library/ms972976.aspx

Q&A on viewstate verus session:
http://www.velocityreviews.com/forums/t71973-q-questions-about-viewstate-versus-
session.html

Generally, the approach is to use viewstate preferably because session
adversely affects performance - holding user control states beyond the
point their relevant is an obvious risk when using session - but if
page load begins to suffer under the weight of a larger viewstate then
it's time to look at the alternatives. Anybody want to chime in with
solutions for page bloat?

Kofi Sarfo

Robert,
This is really an ASP.NET newsgroup question, not a c# language group one.
In general, it's not a good idea to attempt to store an entire control
object in either ViewState or Session. You should store values - simple types.
Viewstate only works for the same page, to persist through a postback.
Session works user-specific and persists across multiple page requests.
-- Peter
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