I get the same problem when I use sudo cpan as not (I figured I shouldn't need root access for the i * query). The issue seems to be a recursive loop in /Library/Perl/5.8.6/darwin-thread-multi-2level/Compress/Zlib.pm as evidenced by the "deep recursion" message, followed by a loop which uses little CPU time but nevertheless ties up the system something fierce. When I let this run a while, it finally ends as follows:

Deep recursion on subroutine "Compress::Zlib::AUTOLOAD" at /Library/Pe
+rl/5.8.6/darwin-thread-multi-2level/Compress/Zlib.pm line 87.
perl(274) malloc: *** vm_allocate(size=234504192) failed (error code=3
+)
perl(274) malloc: *** error: can't allocate region
perl(274) malloc: *** set a breakpoint in szone_error to debug
Out of memory!
Segmentation fault
[download]

...so it would appear, what is happening is a recursive loop that is eating up virtual memory until finally it fills the swap. The messages about this and that function or constant being redefined might be symptomatic or might be just noise -- however, I have never seen those on any other system, and they make me suspect there is something wrong with this installation. FWIW -- a user of the same OS level on a MacMini has no problem with cpan. Here's the o conf:

CPAN::Config options from /System/Library/Perl/5.8.6/CPAN/Config.pm an
+d /Users/dcortesi/.cpan/CPAN/MyConfig.pm:
    commit             Commit changes to disk
    defaults           Reload defaults from disk
    init               Interactive setting of all options

    build_cache        5
    build_dir          /Users/dcortesi/.cpan/build
    cache_metadata     1
    cpan_home          /Users/dcortesi/.cpan
    dontload_hash     
    ftp                /usr/bin/ftp
    ftp_proxy          
    getcwd             cwd
    gpg                
    gzip               /sw/bin/gzip
    histfile           /Users/dcortesi/.cpan/histfile
    histsize           100
    http_proxy         
    inactivity_timeout 0
    index_expire       1
    inhibit_startup_message 0
    keep_source_where  /Users/dcortesi/.cpan/sources
    lynx               
    make               /usr/bin/make
    make_arg           -j3
    make_install_arg   UNINST=1
    makepl_arg         
    ncftpget           /sw/bin/ncftpget
    no_proxy           
    pager              /usr/bin/less
    prerequisites_policy ask
    scan_cache         atstart
    shell              /bin/tcsh
    tar                /sw/bin/tar
    term_is_latin      1
    unzip              /sw/bin/unzip
    urllist           
        http://www.perl.com/CPAN/
        ftp://ftp.duke.edu/pub/perl/
        ftp://cpan.uchicago.edu/pub/CPAN/
        ftp://archive.progeny.com/CPAN/
    wget               /sw/bin/wget
[download]

I don't usually mess with the system perl (via CPAN etc). I build my own version from source for development and customisation. I think it's generally a good idea to leave the system perl alone.

(system perl = the version installed by your UNIX distribution from the official packages)

i can confirm that this problem exists in the macports version of perl, which is in theory completely separate from the system perl. i've got the same problem today: macupdate copied a bunch of PPC perl modules into my new intel mac. i finally gave up on trying to fix the system perl, but this seperate perl install is no cake either ... i will try the renaming suggestion above.