I've met a couple people who still alternate between smoking and shooting, even after they've IV'd...personally, when I was still using tar regularly, I'd alternate between smoking and shooting. Smoking eventually began to really irritate my lungs for some reason, so I eventually settled on IV (all day err'day). For one girl I knew, smoking was her preferred ROA even though she'd done her fair share of shooting before.
Was never the case with meth, though. With that one, anyone who shot always preferred to shoot up if given the choice.
Also, with tar people seem to stay away from the needle longer than when it's powder, "real heroin" (diamorphine). I knew one lady (my first dealer) with a 10+ year tar habit, in and out of methadone and bupe programs, and she still smoked. Maybe that's just a misconception I have based on limited exposure to "east coast powder", though...I'm sure that there are plenty of people with really long habits, who are content to simply snort their drugs...