Hardly anyone does any meaningful research during first year. You spend a few months meeting with potential mentors and nailing down a project, then about 85% do research the first summer. After that, you squeeze in research time whenever you can. It's hard with basic science work, but clinical research can often be done electronically from anywhere. The requirements are lenient and the school understands if your quarterly report is thin because you were on medicine and surgery back to back in third year. As a general rule, research in medical school should be small and targeted in scope, unless you want to take time off.
I like the vast resources for mentorship, research, shadowing we have through UPMC. The curriculum has some rough spots, but overall works really well, imo. The classes in recent years that I've observed have all been very close-knit.
On another note, if anyone has the MSAR and doesn't mind doing a small favor for me, please PM me!