Several people complained that Compiz 0.5 did nothing for them, while it is supposed to bring lots of shiny effects. The reason is that most plugins are disabled by default. They should be enabled using gconf (for instance using gconf-editor or gconf-tool), in key /apps/compiz/general/allscreens/options/a
One correct config may be set with
$ gconftool --set /apps/compiz/general/allscreens/options/active_plugins \ --type list --list-type string \ '[gconf,png,svg,decoration,wobbly,fade,minimize,cube,rotate,zoom,scale,move,place,switcher,screenshot,resize]'
At least gconf, png, svg, decoration, cube, rotate, place, plane, wobbly, scale are usually interesting. But, there are dependencies between plugins, so you need to place them in a correct order in the list. Each plugin has a require option which tells you which other plugins should be loaded earlier.
The decoration plugin is pretty important since it takes care of adding window decorations (i.e. borders). Disabling it is generally a bad idea if you want to get a usable window manager.
There are many other options.
Update: Now that compizconfig-settings-manager is in unstable, you might want to install it and use ccsm to configure all this through a graphical interface instead of playing with gconf.