I have a 19"/17" wheelset with Conti Road Attacks on them. I spoke with the guys at Woody's Wheel Works and they helped me make the decision not to go with 17"/17". I like the smaller wheelset on the road; I dunno if it's just a "power of suggestion" thing, but I feel a lot more confident and I think I am a bit quicker through the turns. I am certainly no expert rider.
One thing I hadn't considered is the smaller wheel sizes making the bike so much closer to the ground; I usually park the bike on the centerstand. I haven't altered the stock height in any way. I don't intend to add any length to the sidestand as I probably won't have the smaller wheelset on very often.