[Boost-users] [spirit] parser trees

Just a couple of "noob" spirit questions for you all which are more experiences in the zen ways of Spirit. If I chose to use a parser tree (or ast) instead of cluttering my code with semantic actions, is there any trade off in parse speed, besides the obvious tree generation itself? Now, let's say I generate a parse tree, and output the results to some sort of XML or structured format. Would spirit allow me to regenerate the tree from that format? i.e. Are there any issues/complications with generating the tree manually? What is more common, an AST or a parser tree? I understand the technical differences, but not the reasons behind them (yet). Thanks in advance.