Hi K. -
My kids started this at two, so your son is still an 'angel baby' LOL... You do need to keep a concern on this, but it depends on what he's not listening to - he's figured out that he has autonomy... free will if you like. This is where you pick your battles - but you do have to maintain the control - otherwise the next thing you know, you'll have a 16 year old that doesn't think they have to do anything you say (you've seen those kids!)
If he doesn't want to, say, wear a coat when you tell him to, then no one gets to go anywhere until the coat is on. This can be a problem if you actually have to be somewhere. If it's that he won't pick up his toys when he's told, then I found it really effective to pick them up and put them away where he doesn't get them back for a while.
Just keep in mind that physical force won't work when he's older, so if you force him to put the coat on (put it on for him) then you're setting yourselves up for 'loosing the war' when he's bigger and stronger than you are. If you let him get away with not obeying, you're setting him up to be a poor adult (what happens if you don't do what your boss at work tells you to?)
LOL..no one said it would be easy - they really make you work your brain!
Good Luck