We do the same thing in the AM & at bedtime. Most of the time DD will wake up and self-entertain and/or do cute babble for a while. She'll turn on her Flutterbye soother. So when we hear her babble or when we hear the music from the soother, we know she's awake and happy for the moment. It's like a "snooze" button on the alarm, lets us slowly wake up and get to her. DH usually does the morning shift, so it gives him time to brush, get dressed, & get breakfast ready before picking up DD. It's such a nice way to ease into waking up in the morning, not like the immediate cries to be picked up in the early days.
I don't think DD is actually playing in the crib after we put her down at bedtime, but she sometimes turns on the soother and/or babbles to try to work out falling asleep on her own. Like you, we just let her be unless she's having issues and crying.
After all the difficulties getting her to sleep in the early months, it still feels weird today when we put her down in her crib at bedtime, and she just stares at us calmly while we walk away.
