I chose not to do so because I didn't like looking up at my TV.... I stood it up there on the mantle for a few days to test it out and it really started to annoy me....even though it wasn't THAT much of an angle (modern fireplace, newer house, not a true mantle like the old days)
I have seen it done several ways though.... the 2 most popular are
1. Install custom racks next to the TV, mounted to the wall to hold all your components.
2. Put the components either inside a nearby cabinet (with UHF remotes or one of those mesh screens to allow IR to work), or on a rack next to the fireplace, with the wires fished through the drywall.
I have also seen components placed on the opposite wall (behind a wet bar, for instance) with HDMI cables fished up through one wall, through the attic and down the other wall... good luck doing that yourself though.