[Hampshire] SPF Best Practice

Do any mailserver admins have any advice about SPF? At one point I lead to
believe that SPF was very much the thing to do, but concerns were raised mainly
on the grounds that it doesn't work very well with mail forwarding and the
extensions proposed to solve that weren't in widespread use.

Does anyone know what the situation is now? Has SPF adoption increased or
dropped? Should I verify SPF records for incoming mail?

One or two of my domains have SPF records; I could potentially write tight
(-all) rules for at least a few more. Should I do this?

Dan