Everything in moderation...  I personally do not make a lot of use of XML at all.  I think the use of XML in standards is beneficial due to the wide array of software tools built to adhere to those standards - eg web services.  Certainly saves time rather than coding HTTP POST, etc

But using it internally when some arrays, etc would do doesn't make a lot of sense.  There's a lot of overhead with string processing, etc.  So I'm not surprised that things slowed down significantly - no XML could compare to a simple array of structs and some pointers...  Hope you don't get too flamed by ppl for saying XML is not the saviour of us programmers/developers/db folk

Cheers