I guess it depends what you mean by hallucinations.
I find you get mild visual distortions (everything looks "wavy" and seems to just keep on moving) and closed eye visuals (cool patterns when you close your eyes) on quite low doses. Mainly, you just perceive things in a different way, notice things about their colours and movements you don't usually see. You might see some kind of "expressiveness" in the bark of a tree that will induce a similar reaction/emotion to a given facial expression. You can also get nice tactile hallucinations (a feeling of vibration all over your skin), aural hallucinations (wispers, sounds coming from everywhere at once), perspective hallucinations (e.g. things that are far look close and small), "balance" hallucinations (you think you're standing up when you're lying down) etc.. at quite low doses.
If you want to actually see a full blown human face growing out of that tree and start telling you the secrets of the universe, well... I don't know to what extent that happens, even on high doses. It might be the best way someone finds to describe a trip where they percieve something with face-like expressivity and some strange form of wisdom within a tree, but I'm not sure it's what they actually *see*.
If someone's talking to a coffee table, they aren't necessarily having mad visuals; they might just have distorted ideas that encourage them to feel that the coffee table is an intelligent presence.
I know I interviewed my bed once on Salvia and it just looked exactly like a bed, but with character. Which reminds me I must dig up the recording to see if it actually answered any of my questions.