Is Mikrotik Router useful for load balancing ?

Yes, simply have multiple gateway as your default route.

yes 4 wan load balancing we can .

Yes, mikrotik is linux software router and useful for any network solution. You see a very good example for load balancing on this video...https://www.youtube.com/watch?v=dnLKyu4_md8

YES , IT IS POSSIBLE THAT ROUTER GO FOR LOAD BALANCING.

Yes

/ip addressadd address=192.168.2.10/24 interface=ether1 network=192.168.2.0add address=192.168.3.10/24 interface=ether2 network=192.168.3.0add address=10.0.0.1/24 interface=ether5 network=10.0.0.0/ip dnsset servers=8.8.8.8/ip firewall mangleadd action=mark-connection chain=prerouting connection-nat-state="" \\    connection-state=new in-interface=ether5 new-connection-mark=NET1 nth=2,1 \\    passthrough=yesadd action=mark-routing chain=prerouting connection-mark=NET1 in-interface=\\    ether5 new-routing-mark=NET1 passthrough=noadd action=mark-connection chain=prerouting connection-state=new \\    in-interface=ether5 new-connection-mark=NET2 nth=2,1 passthrough=yesadd action=mark-routing chain=prerouting connection-mark=NET2 in-interface=\\    ether5 new-routing-mark=NET2 passthrough=yes/ip firewall natadd action=masquerade chain=srcnatadd action=masquerade chain=srcnat connection-mark=NET1 out-interface=ether1add action=masquerade chain=srcnat connection-mark=NET2 out-interface=ether2/ip routeadd check-gateway=ping distance=1 gateway=192.168.2.1 routing-mark=NET1add check-gateway=ping distance=1 gateway=192.168.3.1 routing-mark=NET2 \\    scope=255add check-gateway=ping distance=1 gateway=\\    192.168.2.1,192.168.2.1,192.168.3.1,192.168.3.1

Yes, you can. 

Such types of Load Balancing in Mikrotik: 

1. Sub-Packet Load Balancing (MLPPP)

2. Per Connection Load Balancing (nth)

3. Per address-pair Load Balancing (ECMP, PCC,Bonding)

4. Custom Load Balancing (Policy Routing)

5. Per Packet Load Balancing (Bonding)

6. Bandwidth based Load Balancing(MPLS RSVP-TE Tunnels)

Yes. Go and read http://wiki.mikrotik.com/wiki/Manual:TOC