networking - For in-wall home wiring is shielded ethernet cable necessary?

I want to wire my house with ethernet. Mostly this is going to before internet access, but also some NetFlix streaming and gaming. I am not running any home servers and not expect to go above gigabit (if that).

We have holes in the drywall from where the electricians have upgraded our wiring (120v), and I want use those to run my ethernet as much as possible. The runs will be around 10m-20m (~30'-60') in length.

So I wondering: do 120v electrical cables generate enough interference to warrant the use of shielded ethernet for home use?

No, up to Gigabit. If you anticipate going to 10GBe, however, that would alter the answer (not so much "from power wires" as "from other network wires", though, in that case).

In general, you should NOT use the same holes through the studs that the electricians ran power wires through - it's an electrical code thing, and might cause you to fail inspection, if your local authority inspects. It's also a good idea. The walls are open, drill some new holes. Heck, you're in for drywall repair anyway, a few more holes in the drywall make little difference if you have some holes to patch already, so add a few if it helps. The logic is effectively that if there was a failure in the insulation (due to mice in the walls or the like) you don't want line voltage and low-voltage stuff inhabiting the exact same space, and then having 120VAC showing up on your ethernet wires.

The specs basically say that network wiring should never run alongside power wiring and if it crosses, should do so at right angles. That said, if at all possible, run conduit and run the wire through it so that upgrading in the future is possible. You might want to run another phone wire later, or maybe cable tv and having conduit would make it possible to just pull another run if you leave a pull string.