I assume you are referring to the Opie Package Manager as opposed to the GPE one.
Generally, Opie's Package Manager (Opie PM) is stable as long as you limit the number of commands you execute. Due to a memory leak in libipkg, which Opie PM uses, each command allocates an additional 1-2 Megs of RAM which is not freed until the program is exited. Once your device's free memory has been used up, Opie PM will crash, which could cause problems if it was in the middle of doing something.
The maintainer of libipkg is aware of the issue, and newer versions of libipkg have improved the situation somewhat (newer version will be included in the next version of OZ).
I believe your device has 32 Meg of RAM, so with no other programs running, you can probably do about 4 installs/removals before you will need to close it down and restart it. One thing I have done in the past is to have System Info running (using the 1st tab, 'Memory') at the same time so I can monitor the memory useage.
The other option is to use the command line utility, ipkg. However, if installing apps to a SD/CF/MMC card, you will need to also run ipkg-link to set up the appropriate links. Also, Opie will need to be restarted for any newly installed apps to appear in the Launcher. Opie PM does these things automatically for you.