Update Oct 2012, See this article also.
When we in Technical Support recommend an index to a customer, that index is captured and an 'article' is written. When we think the index would be generally beneficial and low risk we publish these indexes to web. Unfortunately I don't think there is general awareness that this happens as it is relatively new in the last few months.
I just checked and if you search for 'create index' and filter using Document Type 'Article' and the Release 'R10.0' there are 31 articles containing one or more indexes which have been published so far. Not all of these will be necessary for your system, but it's probably a good idea to make a plan to implement most or all of them to prevent future problems.
A link to the search is here.
You could also decide to identify the longer running SQL in your system and then search for that SQL in the knowledge base for the correcting index or apply specific indexes to address those statements if there isn't an article containing the SQL you've identified already published. If you are having performance problems, opening a case with Technical Support to have a performance specialist analyze your system is also an option.
