Is it okay to plug a power-strip into a UPS?

[Larry Cook]

I've got the APC 500 ES (which by the way is on sale at Staple for $15 off and 
a $15 rebate for a final cost of $29.99), but it only has three battery backup 
outlets.  I'm using one for the computer and one for the monitor.  I'd also 
like to put the router and DSL modem on there.  Any reason I shouldn't use a 
power-strip to add these two devices to the last remaining outlet?

Thanks,
Larry