I love chatting with website visitors too, but Olark couldn't handle it. I have around 150 concurrent visitors on my sites during the day. Olark would silently limit the XMPP bots to 25 or 30 people (I found out about that after e-mailing them, it's now mentioned on their pricing page), and get confused and either send me messages from the same person through multiple chat bots or repeat messages that were sent over and over.

I've switched to SnapEngage after doing a live chat with Noah at AppSumo using their widget on that site and love it so far. Rather than try to assign a bot to every visitor currently on my sites, they seem to only assign a bot when a chat is initiated, which works great.