no i don't solder anymore, and i switched to plastic boxes.
i encountered a lot of eye rolling on here when mentioning it, and not without good reason I suppose.
i apprenticed for an EC who's been in the business 50+ years; its just the way i was taught.
i finally gave plastic boxes and wire nuts a shot about a year and a half ago; it was definitely faster. I think its safe to say they've been in use long enough to be proven safe. As for cost savings; for me personally, the savings using wirenuts was minimal. Either myself or one specific helper did all of the soldering, and he had been soldering for years so I didn't have to teach him or check joints to make sure it was done correctly. The cost savings using plastic boxes was huge.
But honestly, I just soldered, taped, and used steel boxes because it was the only thing I knew, and never took the time to try the "new" way. I still offer that type of installation though because some contractors request it. There are many "old school" EC's and GC's here who still use the solder/tape method on every job.