Is this a "shared neutral" situation?
Typically the connection of 12/3 to two side by side breakers (black on one, red on other) is used to run a 220v line.  A 220v line has two hots - each carrying 110v - pulled from adjacent breakers on the panel.  In such cases, the single white line is the 220v Neutral.

Speaking electrically : 
What this guy did was use 12/3 to carry 220v to a junction box where he divided it back up into 110 - which should be fine because in reality the 12/3 is two parallel 110v lines, with a single neutral.   The single neutral isn't really a problem here - ultimately all lines share a single neutral back at the breaker box.  In your case, the shared neutral stops at a junction box - and the lines to the outlets are on their own neutral lines.

Are there any hazards to the receptacles?  No, as long as they're wired properly its no different than connecting the neutrals back at the neutral bus bar.

Speaking in terms of CODE and what's allowable - I honestly don't know if it's legal or not, but I cannot think of a reason why it wouldn't be.  The junction boxes are accessible, and using 12/3 to carry 220v is legit, and each outlet is wired to 110 properly.