I've been reading about a few bloggers moving off of manila or Radio. Here's the basic formula for when to switch.

When you add up the:

• Current value of my blogging tool
• Expected value of the stream of improvements to my blogging tool
• Cost of switching

And find it is less than the:

• Current value of an alternative tool
• Expected value of the stream of improvements to the alternative tool

Then it will be time to move.

Every product manager faces this formula.

Dave Winer leaving UserLand is a blow to the future value of the product. His radar for novel technologies and software architectures kept exciting new features coming every month for years.

One of John Robb's challenges: making and keeping the promise of an exciting and valuable future for the product family.