It's fine. About only time you're not allowed to chain through the device is neutrals on multiwire branch circuits.

As Ron stated. You are fine.

A lot of people do that to keep from over stuffing a box with wire nuts and extra wire from a single line coming in.

When putting multiple switches in a gang box. I'd rather go into the attic and split the supply line in a junction box into the number of feeders needed. That way if, Say for example a switched fan goes bad. You do not have to go without lights until a new fan has been installed or repaired.

Note, the one thing to watch is the rating on the dimmers. Many must be derated if multiples are stuffed in a multigang box. Read the manufacturer's instructions.

I'm helping a friend rewiring part of his house and I found this situation: 2 12-3 home runs, one going straight to the kitchen wall and the other one going to the furnace in the garage. The first 12-3 feeds two recept. with the blk. crt, the the red crt. jumps to the switch box to feed the disp.
Then, the 12-3 in the garage, one crt. feeds the furnace and other crt. goes to the same disp. switch box. to feed the dishwasher. Here is where I see the problem, they ran a 12-3 to the the recept. under the sink and tied the disp to the red leg and the dishwasher to the blk leg and all the neutrals together, is that right, having neutrals together from two different H.R.?

carlogui,
It would be better to start a new thread than to piggy back onto an old one.
I'm having a hard time picturing your layout, but if the neutrals from two different multi-wire branch circuits are tied together (making it a total of 4 circuits sharing one neutral on some part of the wiring) then that's wrong.
But a diagram would help to really get this straight.

I'm surprised that multiple wires under one screw terminal on a switch is considered OK (vs, say on an outlet that has two screw terminals on a side, or a backwire configuration designed for multiple wires.) In fixing old wiring I've found this to be one of the most problematic practices, with one or both wires coming loose or arcing. Even if it's OK by code (and I'll trust the real electricians on that) I wouldn't do it, having seen it fail more than once in practice.

I'm surprised that multiple wires under one screw terminal on a switch is considered OK
It isn't. And if that's what the OP is trying to describe, then he should change it.
I think what everyone else is picturing is either using the screw and the backstab or just looping the wire around the screw and having the same wire continue on to the next switch.

Here's an example of the second case.
The "wires" under the top screws are actually a single continuous wire with it's jacket stripped for a little section.