I've done it quite a few times. First drug, in fact.
I did 375 mg (150 mL x 3 mg/mL) my first time (5 mg/kg) my first time.
The bottle was some Canadian crap called Buckley's that was in my house.
It took 30 minutes for me to have physical side-effects, 45 for it to take effect on my mind.
Mental effects were light-headedness and, of course, the robo-walk (fun stuff).
I chatted online, and that was fun and my mood was generally lifted (I could only feel nice after I puked, which came an hour after drinking the stuff) despite the persisting body-heat, itch, diarrhea, and dehydration.
A few hours in, I decided there was nothing spectacular to this so I went to sleep, but I had lots of trouble doing so. Something really interesting (and also really annoying) happened whenever I fell asleep: my thoughts would drift and I found myself hallucinating/dreaming that I was still on my computer, chatting with friends and browsing the net. Then I'd realize, no, I'm sleeping, and come back to reality (it was annoying because I would jolt up from my resting position, sort of like a reflex)
What's described above is about all I've found/experienced that can be considered 'hallucinating'. Another interesting thing I've experienced, though, was at a high dose of 900 mg (12 mg/kg): it was a mental dissociation where, on the inside, I had forgotten who I was, what I had did, and generally what was going on. But whenever my friend talked to me, my body sort of took over talking to him, and wasn't really confused, while I was still trying to figure things out. (I've experienced the same thing with ketamine, but I wasn't with anyone so I don't know if I'd react to people the same way).
I have concluded that those two things are not worth it at all. That is not to say DXM will offer you more, though. But for me, that's about it and I also have long (3-5 day) hangovers consisting of lethargy, light-headedness, and general not feeling 'normal' at all, which ends up annoying and frustrating me. I had a 'goodbye' trip a month ago, to get rid of remaining lozenges (which I dissolved in water to extract some powder and mix with orange juice, which was easier to drink than syrup).
I never experimented at high doses like 900 mg again (even though I'd really like to) for that reason of the hangovers, and because I had a really bad experience that night because I passed out before I went to bed and my mom found me at 9 AM, with my eyes all red, slurring speech, and walking funny. I had to sleep 'til, like, 9 PM until I didn't show any signs of being messed up, lol. (I sort of convinced her it was because I didn't sleep all night, and she sort of bought it because she's good at denial and she is always harping that I need sleep).
So yeah, try it, but be warned that some/all/more of the side-effects listed could happen, because they did to me! =P