I don't mind the affiliate codes being on them, but odds are - especially with HFS's - I'll be going to the admin to grab the codes & titles & descriptions as you can't possibly know how everyone wants their HFS listed in the newsletter (thus the many, many options in the promo area of sites like yours)
Paysites - sure - makes it easier for me to just slap the link onto my todo list, but I don't mind visiting the admin & checking my stats
As far as how often....as often as you have something meaningful to announce to your affiliates.