@bondsbw: I don't know about the common payment method. My credit card and PayPal are my common payment method :)
On the other hand, I do think the hardware barriers should disappear and are still higher than they need to be.
For content bought on a specific platform, things are a little better: you buy music on iTunes and it synches on all devices, same for xBox Music, etc. However, that does not work as well for otherwise purchased music (ripped CDs for example) and you need to rely on music matching services which don't always work and don't give you the bitrate you want when synching on other devices.
The other week, I bought a non-protected (no DRM) eBook and I wanted to send it to my Kindle Windows app. However, because you need a physical Kindle or an iOS Kindle app (not a Windows one) in order to have a Kindle email address, I could not share the eBook among devices (I ended up storing the file on OneDrive and I had to find an eBook reader app that worked on all my devices). Now this kind of experience can be very frustrating and it is common to eBooks, music and videos (with other file types and particularly with photos the situation is much better, though, for example photos tagged on Photo Gallery will not show the tags on OneDrvie, go figure...).
Ultraviolet is doing something very interesting with video and is a good example of how also DRM protected content could be shared among devices.
Personally I feel that more than full ecosystems (including video, music and eBooks), it would be interesting to improve on online storage, local management apps, and DRM management services...