When I first saw my car I immediately knew this size was the absolute limit. It looks great, but it's right on the edge of getting to big for the car. I don't recommend to go even bigger to 18 inch. It will cause people to say "those wheels are bigger than the car is". I can't blame them, 17 inch allready looks very big.
The wheels are exactly as wide as the car. No strange noises or uncomfy ride. The H&R springs are a bit more stiff but still comfortable. Oh, and don't fit lower springs when having the standard shocks. At least you need the VW sport-shocks. I found out that when the surface of the road gets really bumpy even the sport-shocks can't keep up. I might change that in future.
Big improvement is the handling. It grips like hell and changes lanes faster than my head wants to
I also felt an increase of oversteer. The rear is more loose than it was before.
Steering doesn't become heavier (I was disappointed by that). But bumps and holes in the road are now delivered right into the steeringwheel. Now I have more feeling with the road. But you have to be more alert. Bumps in corners do affect the stability of the car. The tire does a lot less absorption.
Conclusion:
+ better handling
+ H&R still gives plenty of ride-comfort
+ looks awesome
+ Goodyears are feeling very very solid
+ less understeer/ more oversteer
+ girls do look
- need to pay more attention when on bad roads as the car is more keen on changing direction on bumps
- more oversteer (can be critical when right on the edge and not used to opposite locking)
- wheels are on the edge of the car, easily get damaged
Last tip for Aaron, don't go for 18 inch. On pictures 17 inch seems to be ok. But in reality I was still a little shocked of how big the wheels get when mounted on a small car like the Polo. 18 inch are WAY to big.
If someone likes to see the result, mail me for some pictures at jjelli@zeelandnet.nl
Greetz, Joy
18s are sooo tempting 
on other wheels, they look smaller, maybe the spokes go right to the rim?