I was making THIS little dual buck yesterday. It has MC34063 5/3V3 and LM2575 1.23-12V adj outputs.

And now I realised something watching the schematic, those two diodes share the same ground.

Is that a problem? When it happens that both of those switches are OFF, will each output capacitor push current through both of these diodes?

I also had in plan using those MC34063 when making multiple voltage sources for project, can I do them on the same PCB?

 

Photobucket doesn't work for all web browsers, and its better to just link the photo here anyway (so people don't need to go to another site).

Here's your photo;

Re your question about the grounds; It won't matter that the ground wires of two buck converters are tied together, provided that it also does not matter if the two ground wires of the Vin supplies can be tied together.