The OS X installer comes with an often overlooked (and more often unknown) log window which shows, in very detailed form, what the installer is doing at any given moment (and since is updated in real time, you know that it actually IS doing something).
To bring it up, when you are installing software using OS X's Software Installer, choose Window -> Installer Log or press Command-L. In the log window that pops up, choose 'Show All Logs' (if memory serves, it was 'Show Everything' in previous OS X versions) from the drop-down list and you will see it updating in real time, showing what the installer is doing:
As an added bonus, when the installation finishes, you get stats on the installer actions:
The log has some other "useful" features if you peruse the file; you get to know what was installed where and other tidbits of information that could come in handy in case of a failure.
BTW, the software that uses the OS X installer come in package files (.pkg or .mpkg) that usually, but not always, have an icon like this one:
Note: Remember to always install software from good, known sources ;)
