[RallyDRock]

its not that bad. my girlfriend is very particular with her 05 jetta. I had my winter wheels which are actually stock VW GTI wheels (17") and couldn't resist putting them on to replace her stock 15" alloys. so i stole her car from her job, gave it a full detail and put the wheels on. Well apparently she checks on her car often and thought that is was actually stolen and totally freaked [B)]oops. luckily she saw my pt and realized what was up. funny thing is that leaving work she was on the phone while walking to her car and didnt even notice the wheels (she's blonde btw) until she got home. ok so maybe not the best example but a funny story nonetheless.
Personal experience: I would have to say that to experience what the ride would be like with 17" wheels, inflate your 16" to 40-42psi and go for a drive. Jump up to 18" and you'll really feel the cracks in the road plus you'll lose some economy and have less rubber to protect the rim from damage.