I set it up a while ago and was happy to kill it Parser configuration is not a problem but be prepared to see duplicated tickets, stuck injection due to "bad formed headers" in spam emails, etc. There is a chance that it might work better in Cerb 3 but parser in 2.x wasn't working well.
I don't remember any problems with resource consumption while we were using Cerb v2 except one thing - the only way to inject new tickets was to setup a script that will download messages from pop3 server. This script was taking quite good amount of CPU and memory.
I'm not sure about your preferences and requirements but at least for us Kayako is working better.
Don't recall anything about shell scripts. I remember configuring some crazy-formatted .xml file for mail parser and then setup a cron job to run some kind of cerberus-2.649.Linux-2.4.18-3smp binary pointing it to the .xml file where all the information about POP3 server was provided.
Kayako might be confusing in the beginning but it seems to be working well for us except one thing - live chat - very resource intensive and has number of critical (at least for us) bugs, so we disabled Kayako live chat and switched back to websitealive. Almost no complains about how Kayako handles tickets / KB / tasks scheduling. Also, Kayako offers online demo - try to signup for demo account and take a look at admin control panel - pretty much all configuration, customization, etc is done through the web interface in Kayako.