I just wrapped up a 4 night Trans-Zion backpacking trip with this sleeping bag and thoroughly love this new piece of equipment. Marmot has designed a great sleeping bag for mid-spring to mid-autumn in the desert.
First, the Plasma 30 is extremely light. I knew this when purchasing but its ridiculous to feel it in hand. Historically I have strayed from going too light for issues of durability but....
Second, the Pertex Quantum this bag uses for its shell and lining is by far the most down-proof material I have ever experienced. After almost a week of use and compression I have yet to see a single down feather. I have never used a piece of down equipment that didn't lose at least one feather a trip. Not a hint of this bag giving up a feather yet which means its will keep its warmth rating much longer.
Third, the shape and features on this bag are perfect for my body and sleeping style. The zipper is long enough for ease of use while ending well above the toe-box for thermal efficiency. The draft collar came in handy for my first night when the temperatures dropped to 25F, which only required that add my down vest to keep warm (this bag is accurately labeled at 30-32 for my body temp). And the hood is well designed as well: it has the proper lanyards for cinching while also being fashioned in a way for me to open it up and breathe when side sleeping. I move alot while sleeping and found this bag worked perfectly on my side or back.
All-in-all.....I can't imagine a better design coming from a major company for a lightweight summer and shoulder season sleeping bag. Compressable, proper EN temperature rating, durable and comfortable. And I really can't provide enough praise for the Pertex Quantum they chose to use.
(Per the zipper issues...they seem to be a thing of the past. Never had a problem with the new 2014 model.)