When should I file bugs?

[Thomas Pfeiffer]

Hi all,
when I switched to the Devel image again today and saw things like the file 
browser and encrypted Activities which are obviously in a very early stage of 
development, I asked myself "At which point in the development of a feature 
should I start filing bugs if things don't work the way they are supposed to?"
Of course the reason why you developers merge things with the main branch is 
to give them more exposure, but I also don't want to annoy anyone with filing 
things that look to me like a bug but are actually just not finished yet.
Is the rule of thumb "If something's strange, file a bug anyway to keep track 
of it" or does it only make sense to file bugs if the creator of a feature has 
declared it "ready for testing"?
I want to help as well as I can, so advice here is appreciated.
Thanks,
Thomas