I'm in the same position (Solaris - fully patched/updated, VB 1.6) I can't get a guest XP to see any USB activity either[1]. Therei s a message pops up when I click on a guest that says
The USB proxy Service has not yet been ported to this host
which I guess is just a long-winded way of saying that USB doesn't work - I wish they'd just say that, if it's the case.
On a similar note, the documentation has an error. Page 99 (8.1 VBoxManage) reckons there's a list option called "hostusb". There isn't, it's called usbhost. On Solaris, it just returns <none>, even when
dmesg shows that Solaris can see a plugged in USB stick.
[1] Yes, USB & USB2 _is_ enabled in the VB settings