While I don't have any major issues with VM I will be leaving solely for cost and a few personal gripes. For me it's that one of Sky's offers is about £20 cheaper than what I currently pay so I will going to them and back to BT for phone.
Now I know that there are many supporters of VM here, and I don't want to go down the Sky vs. VM road! But I feel the I don't notice that much of a difference between my old Talk Talk connection and VM's offering, and with Sky chucking it in with their offers I'm going down that route.
My other gripes are that my stb regularly needs rebooting and it won't go beyond 6am the next day!
And I also want the full range of services from Sky ie channels and red button features.
For me it's a matter of choice, not loyalty. It's a consumers choice and Sky are currently offering the services I want at price that is cheaper than my current provider.