I use a fairly cheap Android phone, because I don’t want to give ATT or Verizon any of my money, and I hate cell phone contracts. Instapaper was one of the apps I use everyday that was really hampered by the lack of a native client. Looks like that’s fixed, now.
The interesting thing here is that Marco Arment, Instapaper’s founder/developer, didn’t code the Android app himself. He hired an Android development house to do it. I wouldn’t be surprised to see more iOS-only apps go this way if it works out for him.