I clered 142 with 75% this morning. Mainly the exam is abt: XML Architecture, testing, tuning (deciding which XML tech. is suitable for what kind of scenario....these questiosn will make you think a lot in the exam:-)), Schema's, DTD, Parsing with SAX and DOM, Transformations with XSLT, XPath. I got one question each on XForm, JAXB in the exam. Some parsing questions will ask you about what a particular method ex: startElement() does and you will need to choose 2 from 5 confusing choices. Also, some transformation questions are quite confusing. Unless you have hands on exp. in XSLT you will find these tough. DTD and Schema questions are ok and manageable. A few can make you think hard though.
Here's what I used for studying: XML and related Tech: PHI India - This book is out of print and not easily available. It is a great book and is a great read. Does not cover 142 stuff like Xquery, JAXB but covers 90% of it, so is very useful. IBM 142 pdf tutorials: 5 pdf's for the 5 groups of objectives. Quite nice. IBM 141 pdf tutorial: 3 pdf's. 141 is useful because 90% of objectives for 141 and 142 are same. Innumerable websites: w3schools.com is informative and nice to read, w3.org, IBM developerworks, etc.. Professional XML 2nd Edition: Very tedious and boring to read but is a complete refernce. Can be used to cover whatever is not there in the above. If they can make this book easy to read and understand then this book is all that will be needed for the exam. (Maybe a nicer 3rd Edition...).
I had prior knowledge and experience in XML but not as much as is required for the exam. I took about 4 weeks for preparation. The exam should have been 2 hrs long. It will be really useful if you can make your own notes as you go through the various preparation materials.