I've been using
DVD Aficionado for some time to manage my DVD collection and just started recently with my HD DVDs.
They list 650
HD DVD titles (including announced) and 687 discs as of today.
DVD Aficionado HD DVD
There are 480
Blu-Ray titles listed.
DVD Aficionado Blu-Ray
I'm not sure how they count "titles" but I'm guessing that variants of the same film from different countries are counted separately. I believe that a few may have not been officially announced yet, but many of the past such pre-announcements have come true so far.
I'm thinking that the "disks" number would account for multi-disc sets like
The Planet Earth.
I also use the
DVD Profiler program. They are always delayed by about a week in adding newly-announced titles.
They show 522
HD DVDs (they only list officially announced and already released titles and they use actual UPC codes as database keys).
DVD Profiler lists 437
Blu-Ray releases.
Assuming that each counts both formats consistently, it looks like there are a significant more HD DVD titles world-wide and that the statement that there would be at least 600 HD DVD releases this year will easily come true.
I haven't tallied up the studio data from DVD Aficionado, but I've heard that there are many more studios/distributors (not necessarily all major ones) behind HD DVD world-wide, in the US and especially Europe.