The basic changes to Adsense revolve around the addition of Interest Based Advertising as opposed to the previous Placement Targeted Advertising. You can visit Google for a description of what Interest Based Advertising entails.
As an Adsense publisher you also have the option not to use Internet Based Advertising and may Opt out by following the instructions posted in Google Adsense Help. I do not recommend that you opt out but the choice is yours. These changes should help increase your CTR and CPC in the long run as you will become less susceptable to being smart priced. (ie. Conversions should increase as users are presented more advertisements based on their interests)
It is still too early to give any conclusive feedback on how successful Internet Based Ads are but early results seem to be positive. Unfortunately March was a bit rocky for publishers as all the new changes to Adsense caused a number of glitches – several days saw CTR under-reported which Google admitted was an error on their part as they were not showing relevant ads. They maintained that it was only for a few hours but it lasted several days. You may have also experienced higher than normal pageviews for a few days.
Personally I have seen and am still experiencing strange CPC highs and lows as recently as yesterday. I’m not too concerned as I think it will take a little while to iron out all the bugs and caution everyone to just wait things out for the month of April before making any major changes to your Adsense sites. (ie. Don’t concern yourself with smart price tweaking for the time being)
If anyone has seen definitive results either good or bad regarding Internet Based Ads please feel free to leave a comment.
FYI – I am on holidays with the kids at the moment (spring break here) so have been neglecting my comments but should be back to work next monday.