Is it common for college students to drop a year or 2 between UG and graduate studies?
I can't say if it's the norm, but I don't expect that working for a year or two after undergrad would be frowned upon by graduate admissions committees. So long as your job is related to your field of study, you'll be augmenting your academic studies with real-world experience, which can indeed be valuable in preparation for a graduate curriculum.

Personally, I applied for grad school straight out of undergrad, but didn't find the funding I was hoping for, so I worked for a year and then tried again. I received more and better offers the second time around.