Plenty of 2-person fully-netted single wall shelters in the 2-lb range, or lighter for solo. The key is the materials - silnylon or cuben fiber and use of hiking poles (and/or small tent poles).
TarpTent by Henry Shires ZPacks Cuben Fiber Shelters These are a little heavier, but still ultra light:
Six Moon Designs Tents This system is very modular, slightly heavier than others, but more durable:
Hyperlight Mountain Gear Then there's the tarp-only solutions, which are the very lightest, best ventilation, but no bug protection, no privacy, and subject to wind issues. Often that's just fine for summer in the Sierra Nevada if you're willing to ride out the tough times.
As stated in a previous post, these high tech materials are expensive. The companies are small to mid-sized with excellent service, but some products are so popular they have wait times of weeks or months to get.
