Deutsche Post has been private since 1995, and gradually bought itself into DHL as well. I don't live in Germany so I can't tell if things have gotten better or worse.
In the Netherlands, the post office has been private since 1989. From people I know in the Netherlands, things have been going downhill since, especially in the last few years with TNT. Philately is not what it used to be also.
Here in Portugal, they're discussing the possibility of privatization. I fear it will have negative impact.
I sure hope
Canada Post doesn't go that way.
For sure postal administrations have a profit view of things but that view doesn't entirely blind the criteria of philatelic management. However, when you're purely private and depend on shareholders and their money, sometimes you start thinking a stamp with burgers sells more than a stamp with a historical moment of your country.
When that starts happening, that's when stamps lose my interest. I can stand a Homer here, homer there, but definitely not Homer everywhere. If I wanted that I'd collect Panini sticker albums like I did as a child!