I did some calculations and found that a tarp, ground sheet and bug net big enough for me and my dog weighed the same as my 2-person tent (more like a 1.5 person tent, but comfy for Hysson and me.

Of course for the PCT you probably aren't taking a dog, but you still won't save weight using a tarp instead of a tent. There are a number of one-person tents weighing 1.5 lbs., including the Tarptent Contrail, Six Moon Designs Lunar Solo or Skyscape Trekker or (for quite a bit more $$$) no more than 1 lb., such as the ZPacks Hexamid or SMD Skyscape X.

You will definitely need that bug net for a fair-sized part of the trip, especially in Oregon. If it's a late snow year, probably parts of Washington, too! Think of many plateau-like areas on the crest full of small lakes and bogs--mosquito heaven!