wrt slj4j in jclouds, I've considered it. Personally, I'm not a big fan of using the classloader as a DI tool. I do like the recent shift to null loggers, which we did over a year ago. However, there's really never been a log-related feature we've needed and are lacking.
More importantly, slf4j isn't defacto: rather it is one of several popular log apis. While light, it still represents a dependency those who just use log4j, java logging (or run in google appengine, android, etc) wouldn't care to bring in. Log veneers are extremely short and easy to maintain code. It is an easy burden to accept on behalf of the users.
That said, we will make a slf4j adapter, so that those who use it can have that supported in jclouds. That makes total sense and I've logged this below: