There are very few things that will cause any program, including Poser to freeze at Random...

One is an issue with the Program, but this would affect all users fairly regularly.... if this is not occurring, then you need to look at other causes.

System is not up to date. This includes Operating System, Browser (IE for Window Users, even if you do not use IE as your default Browser), Software Updates, Drivers, other application Updates, etc... You should always reboot and check for System Updates and other application updates again. With Vista and Windows 7 (and on XP when using some Security Software) I recommend downloading updates but installing them under Diagnostic Mode/Safe Mode.

Clean up your system.... I know there are those that do not think this makes a difference, but there have been articles in 3D World, PC World, etc... that say if you Defrag a Drive, even very large (fairly empty drives) there is a performance boost. My monthly steps for this is I run Clean Ups, Scan Drive, then Defrag Drive, then reboot. I have had one user recently that reported an issue with a specific Scene cleared up after doing this. I personally do not think that impacted the Scene File itself, but other resources the OS uses that was leading to the issue (Memory Errors when Rendering)

Conflict with other Processes. To rule this out, or locate the culprit, use MSCONFIG on Windows or Safe Boot on MAC to limit Processes to only those required on a system. If the issue does not occur, then you need to do some additional testing to locate the cause, like the user mentioned System Mechanic. Normally once located, users can find a setting that they can change and the issue is resolved. These types of issues are hard to test when we do not have the software.

One note (and I have replied to the OP directly).... When deleting Preferences seems to fix the issue for a time, you can be sure that the corruption of the Preferences is the culprit. The trouble here is finding out what is being corrupted and more importantly what is corrupting the files (or more specifically, which file) When you do find a temp fix, such as deleting a file, Save that file instead of deleting and when you relaunch the program, save the newly created preference files. Send those to Support. We can look at them and see what changed to at least figure out if it is just one file or a couple...

Those that use Custom Preferences (most of us) Save three versions... The bad ones, the Default ones on Launch, and the Customized ones after making the Custom changes and closing the application. This will allow us to see if any specific setting is causing the issue.

ratscloset
aka John