Where did you see random PIDs ? I think all (most?) Linux distros use sequental. http://en.wikipedia.org/wiki/Process_identifier#Unix-like
Process IDs are usually allocated on a sequential basis

Also:
http://www.redhat.com/archives/redhat-list/2004-August/msg00004.html

http://lists.freebsd.org/pipermail/freebsd-security/2010-February/005549.html

I am running Ubuntu with 3.8 kernal, PIDs are sequental.
Also, I think there can be problems with some software, when recently-used PID re-used too fast.

In reply to Re^5: forkManager PID 1 less than top by vsespb
in thread forkManager PID 1 less than top by MAR99

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