Volokh comments on the library internet filtering case:

In my view, the court is at its strongest when it argues that library filtering is unconstitutional simply because it blocks too much material.
http://techcentralstation.com/1051/techwrapper.jsp?PID=1051-250&CID=1051-060602A

I agree with most of what he says, but IMO this part of the court's opinion
is weak also. First, there is an escape clause for adults:

“[a]n administrator, supervisor, or other person authorized by the certifying authority . . . may disable the technology protection measure concerned, during use by an adult, to enable access for bona fide research or other lawful purpose.” CIPA § 1721(b) (codified at 47 U.S.C. § 254(h)(6)(D)).

Libraries could easily give an access code to turn off the filtering to
any adult who requests one.

Second, the argument hinges on the filters not working very well.
I don't believe that filters are necessarily so bad. Google has a
porn filter, and it seems to work ok. (You can turn it on or off.)

Third, the court is willing to separate the funding from the filtering
(and let the libraries keep the money), but not willing to separate
the issue of filtering for minors.

Filtering for various purposes is increasingly popular. Eg, blocking
spam, pop-up ads, P2P protocols, potential hacker attacks.
If a library runs a simple firewall, then probably some constitutionally
protected speech will be blocked. Is it now illegal for a library
to use a firewall?