Having only started doing Audax's this year, have only found a few thing to dislike so far.
Payment via Post / SAE, the Paypal route is much easier, quite happy to pay a small premium for this, also avoids loads of posting, as all but the return of the Brevet card can be done via e-mail
Route sheet in miles, also goes for the whole road system, KM's are so much easier to deal with.
Consistancy in route sheet design, have done about 10 so far this year, most have stuck to the same basic formula, but one or to have been different, but have enjoyed doing the rides.
The early starts and almost everything else I can deal with.