I agree, PEAR does support many DBs, I use it with PostGreSQL (far superior to MySQL
) everyday. Although, I only tested this with MySQL because I know that is what 99.99% of the OOTP community will have and my time is limited. I'd be very interested to hear of success stories with other DBs. Problems will likely arise with some non-standard SQL DBs because CREATE TABLE constructs in non-SQL standard DBs are usually somewhat proprietary.
In my experience, any shared hosting company I've dealt with had PEAR installed by default. But I'm sure there are exceptions out there.
It has been GPL'd, so anyone could of course convert the code to use the dependent mySQL php statements instead of PEAR. But the fact that I used PEAR will even make that easier, because they could simply make their own DB.php class, implement a handful of methods, put it at the same directory level, and my code would pickup their DB.php and not PEARS and make the DB dependent API calls instead of using the real PEAR DB.php.