What is Tivoisation. I would direct you to websearch for indepth explanation or the text of GPL V3 would be more suitable if you are reallllllly interested in this topic.
As a layman's explanation, Tivoisation is the situation where a hardware vendor though is in compliance with GPL v2(That is, the source code for the GPL'd code used in the hardware is released back to the community in the same license, you could call it the "firmware") does not allow the users or buyers of the hardware to flash the hardware with modified firmware compiled from the modified firmware source.
Let us say, U have bought a dvd player, whose firmware is built up completely of GPL'd software. Now, U download the source published by the dvd player manufacturer and put some programming effort in adding additional functions/capabilities to the existing ones. Yes, U have done a great job. Now u have to flash the device with this additional capability. But, stop, U cant do it. The manufacturer will not allow this and probably if you go ahead you will lose your warranty.
Now, there is one more side to this. A rival company wants to manufacture a similar dvd player. He gets the hardware pieces which are similar form standard vendors. He will take this improved/updated firmware created by the individual and flash his device with this. So, You have a dvd player with additional capability in the market for the same price.
Is this desirable. Yes. It is very much desirable. If the initial manufacturer had a broader view of the word "freedom" he would have accepted the changes and incorporated in all the dvd players and provide a free update to all the existing users. The world is an excellent place to live in. If he doesnt want to do it himself he should allow the programmer to flash his improvements on to the hardware. The user payed for the hardware also. He has all the rights to get the last drop of performance from his device. The manufacturer should not lock the device down for further improvements. The customer should have the right to modify/improve the device he has bought. The customer should be "free" to incorporate the improvements and also share the same with his friends and in turn upgrading his device also.
I am against Tivoization. I understand my device better. I know its capabilities. I know how its use can be extended. If I dont know my friend knows. I want to incorporate his improvements on my device. Its my device. I should be free to use it and improve it. Damn the warranty. I liked the way, RMS thought about the whole issue of tivoization. I know Linus torvalds doesnt like this. He wants the Linux kernel on the majority of platforms/devices. Time is the only answer to these disparity of views. I am happy that RMS detected these issues and added corrections in GPL v3.