1. Clinicaltrials.gov identifier numbers will appear in PubMed records when the original publications include them. This will allow cross-referencing between PubMed citations and Clinicaltrials.gov. (Unfortunately, the cross-references will not be "clickable" so you'll have to look 'em up manually.)
2. Author names in Citation and Abstract formats will now be clickable. Hover the cursor over an author name and a mouseover box will pop-up, instructing users to click on the name to search for other citations by the same author. Keep in mind that the "same" author may be the same only in the sense that names are the same.
3. Search terms will now be highlighted in PubMed. Enter search terms in the PubMed search box and the terms will night be marked in pale yellow. The really good news is that this feature is available not only in the Abstract and Citation displays, but also in the Summary display format, the default in PubMed.
4. PubMed's online help document (located on the blue side bar on the left-hand side of the page) is being replaced by an enhanced "book" in the NCBI Bookshelf. The good news is that the help book will be searchable from the Entrez search box (just as one would search PubMed.)

So, for more of that information, go to the Technical Bulletin:
http://www.nlm.nih.gov/pubs/techbull/current_issue.html

Keep in mind that this link will take you to the Current Issue, which, for only a few days more, is the May-June issue. If you don't get there before the end of June, you will need to look up these articles in the past issues.