It really depends on what part of the public service you are in and your role. Some of it pays better than the private sector or has a nice cushy job, and other parts pay much worse.
ABout 8 years ago I joined the PS as a just-out-of-Uni graduate doing IT. At the end of our 12 month "gradate" program we were APS6, which is the highest non-management band. Want a pay rise more than the small increments or a promotion? You have to move to EL1 which, even if it's "technical EL1" and has no management responsibilities loses you paid overtime (work weekends for free), flex time, etc.
Or do what most people do, and quit to go to the private sector. I think from my graduate intake, there were only 40% of us left in the public service after 2 years (12 months after the end of the grad program). Myself, I lasted 2.5 years before I left for a job paying 40% more than my public servant salary.
The bad thing about the public service is that it's almost impossible to get fired, which is why you get the lazy wankers who coast by for years on an average wage. If you're good at what you do, the public service isn't the place for you