The only time my beer touches air post-ferment is when I take hydrometer samples (often only once per batch, sometimes a few more if things are slow), and when I rack to a keg (avoiding splashing of course). If your process involves SIGNIFICANTLY more air introduction than that, then I'd guess you would need to reevaluate what you're doing, but otherwise I would not worry about it. It's certainly possible to oxidize your beer if you're careless, but the majority of homebrewers have a pretty similar amount of air exposure in their standard processes and don't have any problems. With the number of BJCP-certified beer judges present in the homebrewing community, any significant oxidation that occurred with normal brewing practices would not go unnoticed.
If you want to train your palate, you can intentionally oxidize a bottle of beer and do a side-by-side comparison. There is info out there on intentionally oxidizing the beer to help you study to become a BJCP beer judge (as well as reproducing lots of other off-flavors), try googling it.