This year is the first year of JavaOne under the umbrella of Oracle and it takes place in the same city and the same week as Oracle OpenWorld: September 19th - 23rd in San Francisco.
You may ask how Oracle can host two conferences of that size at the same time in the same city: Moscone Center (for me the home of JavaOne) is now the home of Oracle OpenWorld whereas JavaOne has been relocated to the so called "The Zone" consisting of three large hotels, all near Union Square (see red markers in the following map):
View JavaOne 2010 in a larger map
Registration is open for both conferences and both do offer a discount at this moment when registering within the next few weeks.
If you go to JavaOne for the first time you might want to compare it with last year's conference where it was hosted by Sun Microsystems for the last time:
We (the CTP Java Competence Group) are very curious how both conferences will present themselves in this new Java era led by Oracle.