In this article on his Adobe corporate blog, Bill McCoy comments that the eBook format wars are over (nicely timed to tail-gate other "end of format war" news...), and it just so happens that Adobe have the tools to help you create using the new format (.epub).
By all accounts .epub is a step forward from previous attempts at a standard, although you can find some criticisms on blogs of a few short-comings of it.
Adobe does have the leading position in the creative tools, and have been proactive and already has good support for .epub creation in Creative Suite, and for .epub consumption in Digital Editions.
However, it remains to be seen how this emerging standard for reflowable electronic content will reach consumers. It seems that, initially at least, it will be adopted by publishers creating content, and "e-Tailers" ingesting content. This will ease the lives of publishers and content creators, and give e-Tailers (some of whom may also be eBook OEMs) the ability to accept one, standard, eBook format and to convert it to the target eBook's characteristics (display size, resolution, etc) or the various existing eBook formats they support.
But, as eBook OEMs want to control (and monetize) the access to content by their installed base of eReader owners - this standard format may not make it as far as the end eReader device itself, which will continue to access device in its proprietary format (Kindle, Sony BBeB, MobiPocket, etc) and will remain an internal industry exchange format.
As eBook content grows and the market develops then this picture may well change - and agreements will enable a publisher and an e-Tailer, and maybe even a device manufacturer to all get their share of the pie each time an eBook is sold: from any source to any device via any e-Tailer portal or service.....if so, then .epub seems to be best positioned to be that standard for reflowable content, and PDF for final page form content.....and Adobe wins all round on content creation and reformatting tools. Well done!