This is just a heads up that MDB2 is rapidly approaching its first release candidate. This means that the API will from that point on not be subject to modifications and only bug fixes will be applied. Considering the stability of the code I do not envision that it will take many RC's to get MDB2 stable out of the door.
If you look at the current open bug reports for DB you will notice that alot of them are structural issues that are close to impossible to fix at this point. These are obviously all solved in MDB2. Aside from that MDB2 has way more features and is way more flexible. Most amazingly it has been shown to be a lot faster too!
The first two stable drivers are like to be the mysql and mysqli drivers. I am sure Lorenzo will also soon feel comfortable marking the ibase driver stable. The pgsql driver is also looking fairly solid. There are still some issues to solve in the sqlite driver (I heard the metabase driver is now able to emulate a fair number of table alterations that are not possible in sqlite2 that might be worthwhile to port to the MDB2 driver).
The oci8 driver is still missing a fair number of methods in the manager and reverse module. Stability is also far from ideal mainly because ext/oci8 is still fairly buggy (especially when it comes to LOB handling and DDL statement execution).
David has been spending some time on the mssql driver, but I fear its still fairly far from stable. The fbsql driver is now marked unmaintained and needs some serious love.
The last driver is the querysim driver that I will give some attention right this very second. Since it is not quite as feature rich (by its very nature) it should not be too big a challenge to get it stable.
If you are interested in the details on the changes since the last release check out the relevant package*.php files in CVS.