Hi,

Got an odd clearance the other day, on climbout from Santa Monica
(IFR but in perfect VMC): "climb and maintain 6000 when direct
Ventura". I took this to mean that someone would later clear
me direct VTU, whereupon I would climb.

My guess is: he said "c/m 6000 THEN direct Ventura" (so you'd have to climb
to 6 on your current clearance and turn after reaching 6.000)

I wonder what this clearance really meant?

Probably the best guess, whether IFR or VFR is: if you're not 100% sure what
he meant or if you understand everything correctly: ask the guy! Nobody will
grill you for that, and it is a lot less sweat in the cockpit if you sure
you're doing what the controller wants you to.

Happy flying,
Patrick