I used royal mail to deliver 120,000 for me in 2007, lots of fun, and gets the phone ringing, a bit of work involved with labeling the boxes and taking them to their depot and so on, I would use them again, but then i dont need to as I have built a team of leafleters over the years and tend to do around 100k each year anyway.
my team can deliver up to 5k a week, royal mail has the advantage there and can do alot more, they did about 10k a week for 12 weeks for me.