In general terms, fragmentation of Android is a good thing. You can visit your local phone shop and choose your perfect phone from a huge range of shapes, colours and prices – all running a powerful operating system with a huge number of apps available. Manufacturers can produce phones and devices with specialised hardware, like the outdoor proof Defy + (mine recently survived a washing machine cycle), and specialised software, like the Amazon Kindle Fire, but still utilising the advantages of a common operating system and app ecosystem. Even manufacturers producing their own skins is, in principle, potentially a good thing.
However in reality there is a darkside to fragmentation. Just before Christmas my Motorola Xoom was updated to Android 3.2, released in July. To be fair the update was available elsewhere earlier, but my wifi only Xoom, with minimal obvious manufacturer customisations, was updated 6 months after a release. Why did it take so long?