(Boilerplate warning - this info is as of 2015-02-16 only, this info may be incomplete or incorrect, this may not work for you, or your environment)
For wheezy -> jessie users who do not want to manually compile packages AND keep systemd out of the system.
First, go to "options->preferences" menu on the aptitude and uncheck "Install recommended packages automatically" checkbox(or do equivalent on synaptic). This will also make your system more managable(stops installing unwanted packages).
Then HOLD OR DOWNGRADE POLICYKIT-1 PACKAGE TO 0.105-4 - this is the last version that don't depend on systemd related library. If you don't have this version, get this version manually from net and install it using dpkg.
I think all bad things starts from this package. - if you hold this(and be careful), you'll still be able to enjoy many of the improvements of jessie without installing most of the systemd crap(even systemd-shim). After this, there will be 2 problems left to your general desktop user experiences.
One is about login environment -> this relates to the fact that not long ago most of the display managers(gdm3,kdm,lightdm) became dependent on logind included in systemd(again corrected in kdm,lightdm so these 2 are safe again) - if you're paranoid, just use slim or wdm or xdm(since these 3 are ugly, you'll need some additional tweaking) instead and DON'T FSCKING USE GNOME3(gone are the days when one can install gtk/part of gnome2 libs only freely to use standalone(not gnome related) gtk2 programs. Gnome3 become more intermingled like windows) or XFCE4(core functions of xfce depends on libpam-systemd). If you are using LXDE, don't install lxde task since this depends on several packages which again depends on systemd. Install lxde-core task instead and invidual packages you want to use on LXDE(oh, and get/tweak pygtk-shutdown from net instead of existing shutdown button of LXDE to enable shutdown/reboot). Other simple WMs don't need to worry(just worry about DMs).
The other is printing. CUPS on jessie depends on colord which depends on libsystemd0 and policykit-1 so unless you use CUPS on wheezy version there is no simple way to prevent libsystemd0 from being installed on your system, but you can still prevent other systemd crap if you hold polcykit-1(systemd, libpam-systemd, etc.)
Packages to avoid like plague - policykit-1(0.105.5 or later) - Unlike others who are helpful about reducing unnecessary systemd dependency, the maintainer of this package is vehement about keeping libpam-systemd(and dropping seemingly still working consolekit) dependency to this nearly essential package for desktop(see bugreport #747105 yourself), libpam-systemd - this package depends on systemd directly even with systemd-shim present on system.