I just realized that two lines of this kind are added every two seconds in my system.log (/var/log/system.log). They are shown on two lines each below to narrow the story width:
Jan 21 01:16:28 localhost mach_kernel: USB: 262.604: AppleUSBOHCI(0x188F000)::It stops if I kill background palm application...
ReturnOneTransaction - found the end of the transaction(0x97C73F0)!
Jan 21 01:16:28 localhost mach_kernel: USB: 262.604: -AppleUSBOHCI(0x188F000)::
ReturnOneTransaction - done, new queue head (L0x97C8180, P0x80F1E801) V0x1E8F180
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020122085645398