If two routes have equal cost will OSFP automatically load balance across them?
Hmmm... Routes with equal costs (ECMP routes) may appear as result of OSPF. But may be created manually.
In any case OSPF doesn't do any balancing itself - it just "creates" and chooses routes between source and destination points.
In the case of ECMP route (doesn't matter - OSPF produced or manually created) usual ECMP route behavior is applied.
If I remember right router randomly chooses gateway from available in the ECMP route.
Balancing is per connection i.e. if packets from point 1 started going to point 2 via gate1, all other packets for this connection will go via gate1 in both directions.
Connection in the Mikrotik is src-address+src-port+dst-address+dst-port.
But every 10 minutes (again if I remember right) connections in the connection tracking table are resetting i.e. possible situation when first 10 minutes packets going via gate1 , next 10 minutes via gate2 and so on. Also it is possible situation when http traffic between same two points will go via gate1, https or ftp - via gate2.
Also possible problem with some protocols like SIP. For them either protocol helpers should be switched on or other methods applied.
If you need something other - you should try other methods from
http://wiki.mikrotik.com/wiki/Load_Balancing
For example, PCC or bonding...