The fact that I was able to act as a Chinese<->Japanese<->English translator with my very poor Japanese, but very extensive gairaigo vocabulary, I was able to get my messages across perfectly. 70% of the words I used when I spoke Japanese was gairaigo. OK, maybe that's a bit exaggerated, but nonetheless saved my behind. I was just helping my friend who had visitors from Japan, so it wasn't something too official anyway. If I stumbled onto a concept I didn't know how to express in Japanese, (katakana) English was there to save the day! It's hit or miss when I speak with my Japanese friends and they use gairaigo. Darn Engrish!
The only language that hasn't really changed is Chinese (characters being simplified is a tragedy though, in my opinion). Too many times have I seen Latin or French or German words being used so casually in English (mainly in prose, journalism, etc). Though they are words that have been incorporated into the English language, sometimes I have no idea what is being said.