Hi Again,
At first, I was thinking of going with WPMU as there's loads of WP themes available, it's user friendly and easy for a person with basic computer skills to use. When you say it doesn't scale well, how many blogs/websites are you talking about before you notice performance hits?
MT opensource looks to be on the way but it may take a while for extensions and themes to come online.
Does MT handle domain mapping?
Thanks for the helpful advice.
Bearaman