Answers here http://wiki.mikrotik.com/wiki/Virtualization
At the wireless ISP client site
- set up two isolated routers and set the wireless control only for the router controlled by the WISP while the Ethernet side router is fully under the clients control
At multiclient sites (such as office buildings)
- in locations serving multiple clients by Ethernet from one backbone connection (wired or wireless), give each customer control over his own isolated virtual router
Now that is smart! I like this idea and will have to try it at some point!
Great News ! especially at Client side 
I tried to create a MetaROUTER on a RB433AH with the test v3.21 package. The CPU usage was too high - 100% with no traffic passing through the virtual router. The CPU usage of the RouterBoard at normal operation is lower than 30%. So I expected to see CPU usage go to 40-50% but not to 100% (even with no traffic).
This could either be a bug or due to the nature of the virtualization, so what I can say is - try to make it more like xen - where only this-and-that is virtualized and most is running native, if this makes sense, I’m no developer, just a virtualization fan and MikroTik fan. And I need all this for work as well 
so Make it.
Regards.
Please make the support output file and send it to support@mikrotik.com
How much ram you used for the metarouter?
Sure. I will do it again and create the supout but later to disturb the Router outside of pic hour usage.
I tried to create MetaROUTER on a RB411A using V3.21 package. After i enabled the wlan1 in RB411A and my router suddenly reboot. Is it a bug too ? Or i couldn’t create MetaROUTER on RB411A?
what configuration you had on that router, as I can’t reproduce your crash? Maybe you could send on the printout of the command that you wrote in the console to enable that all?
So maybe I will have to try it out but I assume you create virtual interfaces then assign them to virtual routers? Then the client could theoretically control the virtual router?
Sounds like the exact opposite of what I want. I would like a master router that can slave others to act like a big route switch. That is kind of how my Riverstone routers work. Each line card has a cpu and performs basic routing, while the CPU card handles configs and functions not handled by the line card. Most traffic does not go through the main card.
One question about network planning. What about the license? Can I put one license on the xen box and use 10 devices inside to test stuff?
if you are running RouterOS with xen package and you create guest RouterOS instances, guests will use the license of the host. That way you can create as many guests as your hardware supports.
I tried to configure a MetaROUTER into a RB411 (32MB) with 3.22
After adding the Virtual router, the main router crashes. Restarting it’s slow and not really reliable.
16MB for the Host and 16 for the vm are definitively not enough i guess so i have to discard the idea of virtual router for our customers (everyone with RB411)
Am i doing something wrong or MetaROUTER is not recommended on RB411? 
if you reduce feature-set that you are using - then you will be able to use metarouter on RB411. But really you have to shave them to bare minimum.
what is bare minimum?