I'm currently working as a PT Sup as I went against Tooner's and many other people's sound advice. Coming into UPS only a few months ago, I was flagged by management as soon as I started to become a part time sup because of my previous management experience, and computer skills. Make NO mistake, you will be abused, but it's not bad if you dont mind unloading, sorting, loading trucks, breaking jams, taping boxes, running irregulars out to the belts (read:contract work), taking crap from hourlys who instantly hate you from the word 'go', even if you were cool with them beforehand, and taking crap from management who expect you to 'get it' even when you have your head IN the work by "WORKING" 5.5 hours a day.
Article 2 Section 7 of our Union contract deals with supervisors working, its absolutely forbidden, because you're taking work from someone who should be hired. But good luck on finding someone to 'write you up'. trust me, I've asked around. The usual excuses for not writing a Sup up are "They might mess with me afterwards" or "I will IF they start messing with me". Hopefully you're in an area with a strong union presence and you wont have to deal with this. Its not that I'm lazy, heck I dont mind the work, its just, by definition, its not what I'm supposed to be doing! It's impossible to 'supervise' or 'learn the operation inside and out' when you're concentrating on being safe, fast, and efficient. And it really burns my butt that they're sending people home when we're "fully staffed", then making me work instead. THAT is every kind of wrong.
If learning every facet of the operation by physically doing the work and figuring out the most efficient way of doing things is your cup o tea, I say go for it. You'll definitely learn much more about the operation than your average worker. But its not by any stretch of the imagination purely 'supervision' or management as it should be. By all means, talk to your current PT sups....ALL of them, seriously, because the working conditions, managers, FT sups are different from building to building. The one REAL question you have to ask them is..."If given the chance, would you go back to being an hourly worker?" I think most of the time you're gonna get an overwhelming YES but your milage may vary.