Following up to my own post, this invocation of the debugger shows just how many symbols were added by CGI:

halfdome.holdit.com> perl -debug

Loading DB routines from perl5db.pl version 1.0402
Emacs support available.

Enter h or `h h' for help.

main::(-e:1):   bug
  DB<1> x scalar keys %main::
0  73
  DB<2> use CGI qw(:standard);

  DB<3> x scalar keys %main::
0  227
  DB<4>
[download]

Note that the main symbol table jumped from 73 stabs to 227 stabs. There's work behind this, and that's gonna slow you down a bit. It also takes a lot of space.

-- Randal L. Schwartz, Perl hacker