Hi DK,

as far as I know, this has not been done yet. This is an important extension to the code, and it will need big enhancements to the data layer too. My 2 cents: you have three options:

1. Extend the core module source code: this is quite straightforward, attach your methods at the end of the updateentry sub and you're done. Create a table where you store the subscribe users and the relative stored procedures. Update the dataprovider to have the data retrieved. However, all this will get lost when the next version will be released and you will want to upgrade.
2. Create a separate module, that uses the Blog module dataprovider to retrieve data. Set some scheduled jobs that check if new data has been added to the blog tables. Store your subscrbed users in a table with fields [UserID][Frequency][BlogID]. You can also create an user interface that shows a checkbox "Subscribe to this bog" and retrieve the BlogID from the querystring, or store BlogID=-1 if all blogs. This would work even if you upgrade / reinstall the core blog module. This way you will benefit all the bug fixes and enhancements that will be included into the core module. Scheduled jobs may be set to run daily and weekly.
3. Clonate one of the core Blog module controls and put it into a new custom module. Edit this control to add your functionality, and hide the original one to visitors. This way you will benefit all the bug fixes and enhancements that will be included into the other controls, but everybody will believe that you extended the core module.

I would go for option #2, definitely. But #3 is not that bad. #1 needs sooo much effort...

Best regards,
Dario Rossa

Option #2, definitely -- with #2 you have a chance at being able to upgrade to future Blog releases .  Also, DK, if you DO work up a nice solution using Option #2, you could make a lot of DNN users very happy if you decided to wrap it up and share it...(pending, of course, the Blog team adding similar functionality in a future release).