We've done the VIP Tour there twice now (2004 and 2006) and I have to say that for us at least, it's a
TOTAL MUST DO!!!
Being a massive TV (HUGE Friends fan especially so getting to see the Central Perk set is worth the money alone!!) and Movie buff, I enjoy recognising areas of the backlot and getting to venture inside the soundstages and see things you never normally get to see. The tour guides are very knowledgeable and will generally tailor the tour to what the guests on their cart (of no more than 12 people - ours have never been more than 8 though) like and will tell you stuff regarding shows and films you like instead of things you're really not interested in like you get on Universal's studio tour.
The tour centre and the tour itself went through a major overhaul a couple of years back and it's a million times better now!!
And you never know who you might spot whilst you're there... we saw George Clooney and Clint Eastwood on our tour last year!

The guides tend to let each other know where they are if they spot them so they can swing by and give you a glimpse.
I'd definitely recommend it. If you enjoy the studio tour at Universal, you'll love the WB studios! And talking of Universal, it doesn't take long to get to one fro the other. I can't rememebr exactly but it was CERTAINLY no more than half an hour or so. We went to Universal after our morning tour at WB and if I remember rightly, it took us around half an hour from the WB car park until we were walking through City Walk on our way to USH. However, I would say that doing both in a day might be pushing it. If you don't mind if you skip a lot of things at Universal, then you'll be fine but for us, it'd never work. Seeing as we make multiple visits to USH during our trips though, it didn't matter.
Anyhow, whatever you do,
have a great trip!!! 