CASE SENSITIVE PASSWORDS
User passwords are now case sensitive, so be aware of that before reporting login problems. Also some security requirements can be also enforced, some by default, such as the use of numbers and letters and password change every 3 weeks or so.
MODULES CHANGES AND MERGES
There are many module enhancements, changes and new global functionality. For example in AP now we have the use of invoice lines, new payments management, TCA for vendor information and enhanced management. MRC now is implemented trough subledger accounting, a new Tax module and consolidated bank management. General information on the changes introduced for release 12 refer to the E-Business Suite Release 12: Release Content Documents note with document id 404152.1 available on Metalink.
WEB ADI
Web ADI is now more widely used and not only for HRMS products. It allows for interaction trough Microsoft Excel with Oracle Applications data, allowing for Query, Insert and Update of information. It replaces ADE for previous releases of HR and ADI for GL. One of the new modules for which it's available is Fixed Assets, allowing for data conversion of Assets trough this technology.
MOAC
Multiple Organization Access Control is a new optional feature that allows to retrieve information for more than one organization from a single responsibility. This requires changes in forms and reports, in order to specify organization chosen and sql and pl/sql modifications to have adequate access to corresponding data. Refer to note 420787.1 on metalink for technical details.
ADF FACES
Oracle ADF is a Java framework used to build the new web pages user interface instead of Oracle Forms, requiring the use of JDeveloper as the tool, so start learning java and XML related things. Some functions previously available as forms now are only available as web pages. No CUSTOM.pll exists, but some kind of personalization is available. Examine functionality is not as we are used to, and more of a debug is required to review underlying information.
Now more official documentation is available, and courses trough Oracle University, as previous 11i release didnt' have a guide on new pages development but only on extension and modification of existing ones.
Consider that for cMRO products family still the older framework is used.
XML PUBLISHER
Tough available since 11.5.10, now many standard reports are built with XML Publisher. This has the main advantage that for example Payables checks only require creation of templates in MS Word for new formats, or eText definition for Payroll Direct Deposit files. The limitation is that only seeded data definition fields are available and some user requirements can't be satisfied, requiring for an enhancement request to Oracle or developing from scratch when we would have expected a way to extend over already existing data definitions.
With custom reports, the issue is that XML Publisher is still a little limited and for more complex data extraction, reports still has to be used, defining XML as output to be able to use it as a XML Publisher data definition.
DEVELOPER VERSION
Developer 9i is required, review new features, and try to identify modifications on developer's guide, which is still basically the same than that of 11i. Some built in calls are now obsolete. There's a migration tool to the new developer version that will make You aware of it.
DATABASE VERSION
10G is the base version for this release. Consider on reviewing the new features as some interesting functionality may be available such as the use of regular expressions.
ON DEMAND INTEGRATION
The latest guide available indicates the use of Interconnect as a tool for integration. For release 12 BPEL is the tool of choice, contact your SDM to have a conference with On Demand people for guidelines on using it.