Not me personally, but I've worked (or work) with many military employees. Most were in the military when they started, but a couple signed up a couple years in. In my experience, UPS is very flexible with military employees. You keep your seniority and your job when you come back. UPS isn't stupid, they know that having military employees helps then look better and terminating someone would be horrible PR and could possibly be illegal (depending on the situation - there are certain laws regarding service members). I used to work with a guy who had Reserves and he got time off any time he needed it for training. If this is something you want to do, do it.