In addition to Oracle's release notes (available on MetaLink, along with the patch), you can find more information here:
http://www.otmfaq.com/forums/f26/new...-metalink-246/ ([NEWS] OTM v5.5 CU3 is available on MetaLink) http://www.otmfaq.com/forums/f26/ins...-cu3-ru02-556/ ([INSTRUCTIONS] Applying OTM v5.5 CU3 RU02)
Keep in mind that CU updates are large and include additional functionality, so considerable effort should be taken to test before moving into production. RU updates only include patches and are therefore easier to test.
Please search the "Patches" section of this forum for more details.
--Chris