I think you're providing a marvellous service and I'm seriously thinking of swapping one of my larger ezines over to you.
I think this is an excellent way to acquire paying customers AND will give many potential users the option to see if they can build a decent subscribership without having to front the $250 or more that would be needed for ListBuilder.
Your system is the best out there! I have used bravenet.com and listpower.com...it is just really easy using your system.