We stiffened up and lowered the front forks, used some fork stops to limit travel in teh front forks and put on a 23" fender. Unless you do a raked tree (we like Pickard) the 21" will ride better. This is due to the nature of the fact that a 23" wheel is so much bigger than the 21".
I live in New England and the crack sealant "black lines on the high way" the front end used to follow those. It was a little sketchy I went to a 19" (fatter tire) and it was all good. Also if you stretch the front end it works better too but I am too cheap for that.
This is how it works... People put the 21" on their bike to look badazz then they say they ride great. They do this so it doesn't look like they wasted all of that money for looking cool.
Get this same crap with apes to... there's always some know-it-all that genuinely believes he knows what you like better than you do. 21 inch wheels on harleys are far from anything new, neither are apes. Guys been riding thousands of miles happily with both for dozens of years. I cannot for the life of me figure out why these morons care about what someone else does to their bike, and even more i can't figure out why they think i'm going to care even a little bit about what they think about what i do to my bike.