If that isn't a ringing endorsement, I don't know what is!
I would go to a good paint store (not Lowes or Home Depot) and find out the best way to seal the wood based on your climate, how much sun/water the surface gets, what the deck is use for, etc. Some typical wood sealers may not be durable when in contact with wood treated with arsenic.
Treated wood can be bad stuff, esepically CCA-treated wood (aka chromated copper arsenate). No matter the treatment, until you get it sealed, I wouldn't let my kids crawl around on it or lay on it for a sun bath, for example. I'll admit I'm paranoid, but I worked as a consultant for the EPA too long.
Here's what the EPA has to say about wood treatments: Overview of Wood Preservative Chemicals. Then here's a special brochure about CCA pressure treated wood: Guidance for Outdoor Wooden Structures Decks • Playgrounds • Picnic Tables