preparing wheezy upgrade, lots of aptitude c-state packages

[Bonno Bloksma <b.bloksma@tio.nl>]

Hi,

While preparing for the upgrade from Squeeze to Wheezy I ran:
-----<quote>----------
linbobo:~# aptitude search "~c"
c   libbind9-50                                                   - BIND9 Shared Library used by BIND
c   libdns55                                                      - DNS Shared Library used by BIND
c   libdns58                                                      - DNS Shared Library used by BIND
c   libept0                                                       - High-level library for managing Debian package information
c   libisc50                                                      - ISC Shared Library used by BIND
c   libisc52                                                      - ISC Shared Library used by BIND
c   libisccc50                                                    - Command Channel Library used by BIND
c   libisccfg50                                                   - Config File Handling Library used by BIND
c   liblwres50                                                    - Lightweight Resolver Library used by BIND
c   libxcb-xlib0                                                  - X C Binding, Xlib/XCB interface library
linbobo:~#
-----<end quote>----------

Now, how do I know whether I need those libpackages or not? After all I am supposed check whether these packages can indeed be safely removed.
Am I supposed to run:
-----<quote>----------
linbobo:~# aptitude show bind9
Package: bind9
State: installed
Automatically installed: no
Version: 1:9.7.3.dfsg-1~squeeze11
Priority: optional
Section: net
Maintainer: LaMont Jones <lamont@debian.org>
Uncompressed Size: 926 k
Depends: libbind9-60 (= 1:9.7.3.dfsg-1~squeeze11), libc6 (>= 2.4), libcap2 (>= 2.10), libdb4.8, libdns69 (= 1:9.7.3.dfsg-1~squeeze11),
         libgssapi-krb5-2 (>= 1.6.dfsg.2), libisc62 (= 1:9.7.3.dfsg-1~squeeze11), libisccc60 (= 1:9.7.3.dfsg-1~squeeze11), libisccfg62 (=
         1:9.7.3.dfsg-1~squeeze11), libldap-2.4-2 (>= 2.4.7), liblwres60 (= 1:9.7.3.dfsg-1~squeeze11), libssl0.9.8 (>= 0.9.8m-1), libxml2
         (>= 2.7.4), debconf (>= 0.5) | debconf-2.0, netbase, adduser, lsb-base (>= 3.2-14), bind9utils (= 1:9.7.3.dfsg-1~squeeze11),
         net-tools
[..]
-----<end quote>----------
And look at the depends list?
If so, the list without version numbers looks like:
libbind9-60,
libc6,
libcap2,
libdb4.8,
libdns69,
libgssapi-krb5-2,
libisc62,
libisccc60,
libisccfg62,
libldap-2.4-2,
liblwres60,
libssl0.9.8,
libxml2,
debconf | debconf-2.0,
etbase,
adduser,
lsb-base,
bind9utils,
net-tools

But how do I know whether any other package needs those libs?
Looking just at libbindx-xx... I also have 
-----<quote>----------
linbobo:~# aptitude search libbind*
[...]
i   libbind9-40                                                   - BIND9 Shared Library used by BIND
c   libbind9-50                                                   - BIND9 Shared Library used by BIND
i A libbind9-60                                                   - BIND9 Shared Library used by BIND
[...]
-----<end quote>----------

Should I run aptitude why against each package?
-----<quote>----------
linbobo:~# aptitude why libbind9-50
Unable to find a reason to install libbind9-50.
linbobo:~# aptitude why libbind9-40
Unable to find a reason to install libbind9-40.
linbobo:~# aptitude why libbind9-60
i   dnsutils Depends libbind9-60 (= 1:9.7.3.dfsg-1~squeeze11)
-----<quote>----------

So should I also delete libbind9-40?

This is the first time I have this many packages that might be obsolete on my system. What is the harm in just leaving them there before the upgrade?
On the other hand I do like a clean system. ;-) Also I have more systems I need to upgrade, I would rather like to understand what to do and why.

Bonno Bloksma