IRShell has that feature, but as you mentioned - it has to be inssataled on both consoles, and that sucks.
Direct transfer via XMB would be great. I guess that the only reason why it is not implemented in sony's firmware are copyrigths issuses (sharing photos is OK, but music not). Transfering via IRShell gives about 250 KB/s speed, that's enough for music and videos (or if someone has many time and battery can copy even ISO).
In my opinion it is on of most important feature, wich M33 CF is still missing. I really don't care about UMD VIDEO, but wi-fi transfer is that what i'm still waiting for.