I’ve tried many webmeeting services over the years and have been consistently using gotomeeting (http://gotomeeting.com).

I regularly try new services where I am looking for more frictionless “adhoc” or on-demand meetings (gotomeeting has delays installing client software and launching the viewer for the participants),  multi-meeting managers services (one master account, multiple authorized meeting managers), and overall lower costs.  Things that are must haves:  low cost, 100% reliable operation, high fidelity screen sharing and audio.

I recently tried “http://join.me” and would not recommend it.   My experiences:

• The  audio bridge quality is absolutely horrible – echo, and poor quality sound.
• The screen sharing response is very laggy for the conference participants and can be pixellated.

At best, the join.me service may be suitable as a free service for internal team use perhaps but certainly not as a paid service, and certainly not for use for a customer presentation or demo.