It seems that it never takes long to find the bad in a good idea; just ask the Washington Post who in a recent article seemingly went on an expedition to find negatives with respect to workplace gyms.
While I'm inclined to accept that the "road to hell is paved with good intentions", I still believe that workplace gyms can offer a lot of good beyond the sometimes shallow reasoning of the WaPo.
If the sundry reasons offered are to be believed, I should be worrying about feeling powerless in my tracksuit bottoms and ragged t-shirt. If one is truly worried about their appearance in the weight room, there are a number of upscale clothing lines for those who feel they sweat differently in expensive gym wear.
The only useful argument against workplace gyms might be the occasional co-worker who doesn't know when to shut up. Your time in the gym is your time and no one else's. So don't give co-workers a chance to disrupt you from your real reasons for being there. If you're too worried about coming off as a boor for asking them to kindly leave you alone, use the iPod defense: take yours out, turn it on, and wander into you own little world.
Workplace gyms may well require a quick refresher course on etiquette, but they offer a lot of people a convenient option for working out at a reasonable price.
They're also a great way to cut the day and to cut stress with a quick power workout before you start or before lunch. Don't let superficial excuses or petty worries get in the way of your health.