None of mine show signs of flowering. You should probably save the seeds in the fall once they fully ripen.

haven't noticed anything

I havent nopticed my spectabilis flowering but I do have some P. aurosulcata 'yellow groove' that seems to be flowering this year. So far only a few within a large grove seem to be flowering but they are full of seed bunches. I filled a large ziplock bag in just a few minutes. I took some pictures of the seed bunches and may post them when i get a minute

Mine have been spreading like crazy, but no flowering, either.
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My Spectabilis is not flowering, either.

Mine is. Bummer.
One of my reference books says that sometimes flowering can be stopped if you remove the flowering culms and fertilize the plant liberally with nitrogen fertilizer. It also says flowering is not always lethal. Maybe someone else here knows more.

Flowering is not very well understood. There are various approaches to trying to save flowering bamboo, but there is no guarantee that any of them will work in particular cases. The link below -- posted on the web site of the American Bamboo Society -- provides an interesting discussion of the phenomenon.

Here is a link that might be useful: When Bamboo Flowers