Hey, this tread is already a little bit old. Maybe someone have some updates.
I've tried to book the tour with mei mei- and mekong cafe. Both don't provide this service anymore to book a ticket for a cargo vessel from jinghong to chiang saen (thailand).
None of them could give me exact informations.
Anybody have further informations and whether they stop the tourism boat transportation because of the massacre in october 2011? Clear informations about the condition of the route are a little bit invisible, most of the updates already 2-3 years old.
Any informations will be much appreciated.

I took it in about August last year.

The number of vessels depends heavily on the season (water level) and there isn't always a vessel waiting.

To be sure, you can call the immigration staff in Guanlei and they will tell you how many vessels are available, since arriving in Guanlei and having to wait a few days for a boat would not be much fun. It should cost about 300-400元/person for a private room with cooked meals included. It is a really nice trip.

PS. When you get the bus to Guanlei from Jinghong consider overnight in Menglun, which has a fantastic tropical botanical garden. They also have really yummy mushroom mi gan (flat rice noodles) near the bus station.

Thank you a lot, I will enjoy the rice noodles.

Seems this opportunity became less attractive, apparently most of the tourism agencies stop all of their costumer booking services since the attacks.
But better anyway to self organize, needn't pay on top for provided services.

I guess they don't have regular ticket counters near the harbor now, how you got your ticket, even negotiated with a captain?