One of the things on my agenda for OSCON (which was excellent, just like last time) was to sit down with a couple of the folks from IBM to discuss why the SDO extensions hadn't taken off as they'd hoped, and what they could do to foster some growth.
One of the things that was apparent was that this SDO stuff has quite a high barrier to entry--too many three letter acronyms for starters, and its origins in the C++ and Java world don't help make it very accessible to the typical PHP developer.
If you've wondered what this SDO stuff is all about, please read through those articles. After having done that, if theres something you're not clear on, or if everything is clear, or if you have some other thoughts on the matter, then please take a moment to send your feedback to Graham Charters (you'll find his email address on the top of the articles).
Graham and the rest of the SDO team would really love to hear what you think about SDO, so that they can work on making it easier to get into.