"They will never guess that your domain name is visual.ly"
No, but they shouldn't ever need to guess. The overwhelming majority of traffic will come from either people clicking on links in email or social recommendations, navigational searches, or people seeing some sort of marketing such as print media or business cards. If people are actively talking about your startup then they'll specify the domain more carefully. Anyone you lose because they go to the .com and immediately give up probably wasn't very interested in the first place.
I would argue that a good, single English word domain with a .io or a .co TLD is going to result in a stronger brand than something that's been crowbarred into an available .com by adding an extraneous word or dropping a vowel.
(I hope so anyway, I'm working on a .io right now. :) )
