Totally agree. Just entering a list of destinations to drive, with the order being set manually, would be step 1.

But... next thing people will want is an automatic optimal solution for this - which can be done, hey, my three year old Mio can do that with up to ten destinations! But here Waze will run into some problems... check this Wikipedia entry on the Travelling Salesman Problem (TSP).

Do not forget that Waze does routing for all those Wazers on its servers. As soon as a significant number of them will use Waze for a list of destinations, routing will take exponentially longer, as to solve the TSP all different travellingdistances/-times must be known and Waze would have to calculate all those on the server and then dispose of 99% of them again....

I can see a solution for most of that in the offline-routing that the waze client tries to do when not connected to the network - but this feature is currently broken ;^((
If it were not broken, the Waze client could calculate the majority of the distances by itself, solve the TSP (or rather approximate a solution) and then let the server calculate the exact routing (including traffic) for the first stretch and then, when arriving there, the second stretch etc.

That way Waze would offer an automatic TSP-solution, and still keep the load on its routingservers low.