Weed Mat, Yay or Nay?

Ok, all you landscape guru's...

We're doing a complete re-do of our landscaping in our back yard... and i'm debating whether to put down weed mat or not. Seems like it's most beneficial on pathways and walkways where there's not supposed to be any growth, but looks like it could be a pain in the arse in the planting beds. couldn't the weeds just take root ontop of the mat? like between the mat and the mulch?

Anyone use it and consider it worth the cost? I've never used it and can say i pull a LOT of weeds during the summer... would rather not have to do that... we get this crap called Nut Grass i think and if you don't get the root/nut out of the ground (i.e. it breaks off AT the ground) it grows back double. and if you spray them, they just sit there dead and you gotta pull them up anyway.

Any other alternatives/ideas?