I'm accustomed to the GUI providing XML output in easy-to-read, pretty-printed form.

I just upgraded to 7.2.1-pre-20120410.144517, and that behavior no longer appears to be the case -- documents (as displayed in the GUI) have no whitespace they weren't originally created with.

Is this an intentional change? Is a toggle available?

Yes, this is an important issue in the current snapshot, and will be updated soon:

https://github.com/BaseXdb/basex/issues/479

The reason is that the serialization code has undergone some minor changes, which have led to the deactivation of the default indentation.

Christian