I was recently playing around with Pallet (as an offshoot of some of the DevOps-style cloud provisioning work I do on Project Clearwater), and had a bit of trouble getting from Pallet to the underlying jClouds API (I was using 1.5.5).
Specifically, I wanted to associate an EC2 elastic IP address with the new node I'd created with Pallet, effectively making it a drop-in replacement for a failed box.
This is the code I ended up with, relying on the fact that pallet.api/converge returns a map with a :environment parameter, which in turn has a :compute object which is a jClouds ComputeService object, which you can do Java interop on:
(let [node-data (pallet.api/converge ...) node (:node (first (:new-nodes node-data))) compute (:compute (:environment node-data))] (-> compute .getContext .getProviderSpecificContext ; AWS-specific function .getApi ;  .getElasticIPAddressServices (.associateAddressInRegion "us-east-1", "126.96.36.199", (.getProviderId node)))) ; 
 .getApi returns an AWSEC2Client, which you can use to access other EC2 services.
 Obviously, this elastic IP was specific to me (and I've since deleted it).
Since then, I've found that there is a nicer Clojure interface to jClouds. I haven't tested it, but the above code should then look something like this:
(let [node-data (pallet.api/converge ...) node (:node (first (:new-nodes node-data))) compute (:compute (:environment node-data)) eip (org.jclouds.aws.elastic-ip/eip-service compute)] (with-compute-service [compute] (org.jclouds.aws.elastic-ip/associate node "188.8.131.52")))