Seems like here that more people wear scrubs every year. Most of the first and second years wear scrubs every day unless they are on CP, whereas it varies in third year and higher (except for a couple of people who are always in scrubs, even on chemistry). Often the form it takes is scrub bottoms and a sweatshirt or some related shirt.
The only real expectation is that people wear scrubs when they cover frozen sections in case you have to go into the OR.
In my day (old fart alert) a few of us would wear regular clothes even on autopsy rotation, and just change into scrubs for the autopsy only. I don't wear them generally when I gross unless it's a really busy day, grossing isn't that messy and you have big cloaks and aprons which cover everything up anyway.
In general there is no dress code. I even see people in jeans now and then and I haven't heard anyone mention it as a problem, although I also haven't heard anyone praise it.
As others may find, these days people get very defensive when "professionalism" is brought up, so if someone mentions wearing scrubs as less professional someone will complain, etc etc, blah blah. But the truth is that your attire does reflect on you. Whether that matters to you is another story, though.