A new paper describes strategies used to select splice-junction targets in order to trigger changes is splicing using Morpholinos.

Morcos PA. Achieving targeted and quantifiable alteration of mRNA splicing with Morpholino oligos. Biochem Biophys Res Commun. 2007 May 8; [Epub ahead of print]

PubMed abstract:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=17493584

The Morcos 2007 paper is now available online as a .pdf:
http://www.gene-tools.com/files/Morcos2007howto.pdf