I use GRML almost daily, sometimes booting it over network and loading it to RAM. We don't use iPXE specificially, but use "vanilla" PXE regularly, too, generally to install systems with Kickstart or xCAT, depending on the cluster we're working on.

I'll be using GRML again tonight to rescue some laptop drives which were retrieved from a fire, to see what can be salvaged, for example. First in forensic mode to see what's possible, then to use dd_rescue on a N95 box.