Just back from another spectacular bikepacking trip on my Salsa Mukluk, I can honestly say that for 90% of my trip needs, a Tarp is the perfect shelter. For the last 5 years I have experimented with tents, bivies, and a number of different Tarps, so I believe that for me, I have acquired a fair bit of experience through a multitude of conditions.
With the exception of some very specific situations and scenarios, the Tarp has ruled the roost. With a bike, I can string a tarp anywhere I want, including the middle of nowhere. Using my technigue for anchoring the bike with line and stakes, it serves as the perfect highpoint for one end of the tarp. The other end can be anchored to some other fixed object, or with the aid of your helmet or stick, stood on end, you have enough lift to comfortably sleep without and contact between your bag and the tarp.
Add in an UL bivy, like one from MLD, and you have bug and splash protection at your disposal. Thus carrying a Cuben tarp, a set of UL stakes and a UL bivy, you are set to string up protection no matter where you travel. With some larger fixed structures to anchor to, you can easily create a very comfortable living space that protects you, your bag and your gear from the elements.
My current Tarp of choice is the Cuben Fiber tarp made by Hyperlite Mountain Gear. I have been traveling with this tarp for almost two years now and it has proven itself as completely reliable. The attention to detail is amazing and the Cuben Fiber is not only light but absolutely waterproof. One very nice feature of Cuben is that it does not wet out. What this means is that after a night of rain, simply shake the tarp and the vast majority of the moisture is displaced, thus keeping your UL tarp in a UL state. I have found that Silnylon has a tendency to wet out and thus your super light tarp is no longer super light and you are stuck packing an item that is soaked through and through.
For those that are serious about traveling light, the combination of a Cuben Tarp, UL Bivy, a Neo Air pad, and a set of UL stakes is the ultimate combination for light weight, flexible shelter. Simple to setup; flexible in how you use it; and a multitude of useable configurations with very few things that can break!