[ QUOTE ]
if they both get to log PIC time whose arse is it if they get in a wreck or a violation?
[/ QUOTE ]The "acting" PIC is the person who is ultimately responsible for the safety of the flight, both in terms of any accident or violation.
In the cases above, the "acting" PIC is the non-flying pilot/passenger who is "acting" PIC during the 3-landings and the SP (remember, both the FP and the SP agreed before the flight that the SP was the "acting" PIC of the flight).
This question illustrates various situations where a safety pilot or non-flying pilot passenger may not want to assume "acting" PIC. That is, the non-flying pilot passenger may wish to remain on the ground while the non-current flying pilot completes his 3 landings to regain currency. During these three landings, the solo non-current flying pilot is thus "acting" PIC and thus is responsible for his own accidents or violations. Similarly, the non-flying safety pilot may wish to serve only in a safety pilot role (i.e. SIC), while the flying pilot (under the hood) serves as "acting" PIC. In this case, the safety pilot may log only SIC time.