Let me say at the outset: I'm an Arcteryx whore. Totally acknowledge it. I'd spend all day in my Alpha SV, in just about any conditions, and do it happily. But there are times when the skies are clear and you're ready to head out, and you're not really sure that you need to pack such a bomber jacket...when you want something light to throw in your pack as insurance against bad weather. You've done enough hiking/skiing/biking to know that if things turn bad, you want a product that will work to keep you dry and warm.
My previous experience with lightweight and "ghost" jackets was that they were light and packable, and some were even waterproof, but when you needed them, they were not breathable or durable. They were bandaids that helped keep you dry from rainfall, but that built up sweat inside like a proverbial sauna.
The Squamish is a pleasant surprise. It's inexpensive (for Arcteryx standards), light and packable--all good qualities in a 'just in case' jacket. but when you need it, it's waterproof, reasonably windproof, and breathable. I'm surprised by how effective a nylon/DWR system can be. 20 years ago, when Goretex was too expensive to afford, the nylon/"waterproof coating" jackets were good for a little rain, and then would get saturated and you'd get wet. Not so with the squamish. It's waterproof. I have had it in some tough conditions, and it doesn't soak through.
Moreover, unlike most ghost jackets, it is breathable enough to actually be useable as a frontline jacket. I find myself wearing it from time to time when I don't need the weight of the Alpha SV, but when I do need reliable, breathable, waterproof jackets. Don't tell Arcteryx, but making good, inexpensive jackets like this undermines the need for their more expensive products, in many 'normal' circumstances. (I'm still not giving up my Alpha). Great jacket! Arcteryx-true sizing, which means it is an athletic cut. I'm 6', 155#, and a medium is perfect.