They have ditched their toolbar as the sole source of their rankings and are now pulling in data from other sources too. This means that the skew towards tech sites (as their readers are more likely to use the toolbar) has been addressed (or at least they’ve tried to address it).
Those who check their rankings regularly will now see new rankings. For some there will be little change where as others will see increases or decreases.
For example my other blog Digital Photography School now shows up on Alexa with a very similar ranking to ProBlogger. Previously it was much much lower despite having higher daily traffic numbers. It’s still not perfect (DPS ranks at 16561 (i’m not sure it used to be but it was in the 20,000s) and ProBlogger 12917 (previously in the 3000′s despite DPS having more actual traffic) but it’s at least closer.
PS: Amit has tracked how the changes have impacted the rankings of some blogs.