Looks like it was successful. Official filing to vacate the initial order mentions the FBI has now accessed the data. http://pdfserver.amlaw.com/nlj/FBI_apple_20160328.pdf

People are guessing the flash ram was cloned, allowing a reset of the possible 10 tries counter. Important to note that the erase after 10 tries is not a default on setting. Looks like the contract from the FBI to a company for $15k was uncovered for whatever process was performed. http://www.macrumors.com/2016/03/23/fbi-israeli-firm-cellebrite-to-unlock-iphone/