ProgrammableWeb just reached 900 APIs listed in it's directory - this is an amazing number since there were just 600 on Jan 14th this year - there's also been a slight dip in growth rate over the summer - with people probably storing up their launches for the fall, so I'd bet on being past 1000 by mid October by the latest (hopefully 3scale will help make that happen!). It's hard to over-estimate how important this is as a trend - programmable web is the reference site for APIs and so provides an important benchmark.
The fact that we're on course to double the number of APIs in what might be just a little over 12 months is incredible. Moores law (18 month doubling) would already be impressive if it was happening - but API deployment is a parallelisable process - not a serial one like chip design - so in principle API deployment could explode even faster.
Look for API "enablers" getting built into standard web tools (from drupal to systems like iceberg and others) - this was the secret sauce of RSS) and then I bet we'll see spectacular growth rates.
Great job to programmableweb as well for tracking all of this!