Zach from Olark here, sorry to hear you were having issues some time ago! Honestly, I'm not sure what could have been causing issues for you back then, but rest assured we take message delivery extremely seriously - whenever you're using Olark if you ever have any issues please let us know so we can dive in to the logs and take a look!

Most of our users routinely have many, many more than 10 simultaneous visitors - I can assure you we work in that case. : )