Ok, well maybe Mikrotik cant replace all the offerings of those companies, but for the small to medium and sometimes large companies, they offer an extreme feature set, rock solid performance and cheap cheap prices.
Last year we replaced all our sonicwall TZ190 all in one firewall units with MikroTik routers. We needed the ability to add useful QoS and actually see what was going on inside our network. MikroTik provided both without fail.
We opted for the RB1100 units which had just been released from production for all our remote sites and one RouterMax(special build) Mikrotik router for the main office. The RB1100's were around $400 a unit and the main unit was just over $1,100. All of the units are 1U rack mountable. All the ports on each were 1Gb, though the RB1100 has two switched 5 port switches in it with 1Gb backbone to the processor and 2 failover ethernet ports.
Most of our remote sites have two connections: A primary fiber and secondary Wireless/copper metro-E, whichever is available at the location. We also separate our wireless, phone and data networks, so having 13 ports to play with was wonderful. Each default install required 5 connections. Our main site actually ended up using all but 1 of the ports due to redundant connections at the site and our local call center thats connected to us by direct fiber.
Anyhow, we deployed some serious QoS trees to make sure our phone networks recieved the best priority possible with data services for our main applications right behind. Next we used OSPF to ensure our backups were secondary routes(and worked), then for our internet connected backups, we ensured firewall and VPN functionality. The rest was just passing DNS to our central DNS servers and the jobs were done.
I would give them a thumbs up for any home or office since they now offer wireless and specialty connections on most routers. I would even recommend you replace that little home retail router from linksys, dlink, netgear or other with one of these units. The one i have at home is constantly humming, i havent had to reset it since i installed it a year ago.