Web service API and caching

Fellow railers (navvies?),

I’ve been looking to integrate some of the functionality of Campaign
Monitor (www.campaignmonitor.com) in our own products and services,
but it seems to me that, for instance, when working with subscribers
and such via a REST API (unlike processing ONE single payment via
PayPal), it would be a good idea to cache the subscribers locally to
make the service a bit snappier and also to reduce the dependence of a
glitch free and lag free connection to Campaign Monitor whilst working
with the subscriber lists (and such).

My question is if anyone has made an attempt at caching such data, and
if so how did you go about doing that, what did you learn (how/when to
update the cache, any problems that might arise), and so forth? NOTE:
Not necessarily limited to Campaign Monitor, but any web service/REST
API which results needs to be or benefits from being cached.

Best regards,
Tomas J.