Esri has released a full Q & A at the ArcGIS Online Blog.
--- update 2/20/11 ----
Update: Faridur Rahman Choudhury, a blogger, offers the text of the e-mail sent out. Matt Artz's GIS and Science blog (not an Esri blog, but he works there: "the postings on this site are my own and don’t necessarily represent Esri’s positions, strategies, or opinions.") also has the text. I am not on the e-mail list in question, it seems.
And, while the data access is free (much of the time), the APIs to access the datasets are not always free.
--- original post 2/19/11 ---
To quote the ArcGIS Online page:
ArcGIS Online map services are available at no cost regardless of use.
However it seems high volume users will still to pay some fees (FAQ):
Yes, ArcGIS Online map services are available at no cost to all users who use less than 50,000,000 transactions per year. High volume users, using over 50,000,000 transactions per year, will be required to purchase ArcGIS Data Appliance for on-premises use or contract with Esri Professional Services or their local Esri distributor for a managed services environment to support their volume consumption requirements.
Back in 2009 I wrote in some detail about the "freeness" of the Esri APIs for the datasets and the datasets themselves.
This change means that now non-commercial use of the APIs is ok if you don’t own ArcGIS Server (whether you are a non-profit or commercial entity). You can use the APIs to hit the free ArcGIS Online data, per its licensing (most is free for non-commercial use, but there’s a fee for commercial use) but all users must pay for premium data. You can also use the APIs to hit any ArcGIS published data to which you have access.
I learned of this via Pierre Crevoisier (@pcrevoisier) and Brian Timoney (@briantimoney) who offer these assessments respectively:
ESRI is changing its politic. ArcGIS Online #map services are available at no cost regardless of use. ...
ESRI freeing tiles a) response to competition--Mapquest, GeoCommons, et al b) cartography as competitive differentiator
It seems the news was dropped on Twitter by @martenhogeweg at 6pm EST on Friday night. It seems all "hot news" comes from Marten...I'm glad he joined the comm team.