It depends on both the employee and the boss - what technical level are they at?
For example, my boss does not care in the slightest about Perl - he just cares that I get the job done on time within budget (I'm actually quite lucky in that regard). Some bosses are far more hands-on and want to micro-manage everything. Then again I have a reasonable track record so the boss trusts me: if you are just out of university then you have to expect the boss to be breathing down your neck. It's a trust thing.

Then there is how much I tell the boss - enough so he can do his own job, much the same as he treats me.