I'm looking to go to Hawaii from the midwest with a flight with 3 connections and two carriers. The price is good but I'm a little anxious about going with more then one carrier. There is a 10 hour layover on the way there and a 3 hour layover on the way back where I switch carriers. I wondered if this is safe if I run into the instance of the airlines losing baggage or if one of the airlines cancels or delays a flight such that I miss the connecting flight with the other carriers.

What happens then?!

I've taken loads of flights with different carriers and layovers. Your luggage should be tagged at check-in for your final destination. As long as there is adequate time between connections your luggage should arrive with you. With 10-hour and 3-hour layovers I'd think that you wouldn't have much risk of missing a connection. As for missing the first flight (or having it cancelled) you might want to call the person selling you the ticket and ask them what happens in that situation. I've never had any problems with flights with multiple carriers, so I expect that you'll be fine.

A 10 hour layover?!
That means total travel time on the trip over (3 connections means 4 legs) has to be at least 22-25 hours!

Direct flights from St. Louis are 8 hours total.

Price has to be REALLY cheap to justify gibving up 2 entire days of travel time. How cheap a deal did you get?

Yeah, 10 hour layover really sucks and so does 4 connections, but I saw a roundtrip ticket for $650 compare to around $1150 to have a more reasonable schedule. I'd like to save the money, I'm just wondering if it is safe to go with two carriers or if this could cause problems.

If you are switching carriers it will depend on what kind of baggage agreement they have if they check your baggage to your final destination. If would be wise to check with the originating carrier as some airlines are not able to through check bags.