As a current Pro user, $25 per year to continue unlimited storage, no ads (for me and for all viewing my photos) and photo statistics is still an easy sell.

However, if I were signing up for an account today, I would most likely not purchase a paid account - my main reason for paying for an account was to get past the "only your last 200 photos are visible" limitation. That said, if I actually used my flickr account for business purposes, I would not hesitate to pay $50 per year to remove ads from my photos. I suspect many professionals would agree.