It matters some what. I find formatting in ebook a big issue and they're certain publishers that do a good consistent job in turning their books into ebook format. One publisher that comes to mind is Harlequin. The formatting in their books are always well done. Harpercollins is another good example with their Avon line.
A Bad example would be Sourcesbook, Inc although they seem to be getting better as of late but I have found their ebooks full of embedded fonts, font size tags and just horribly formatting. I have bought a Kindle version only to have to return it and buy the epub which was much better done.
Another point with me is price. Kensington who has the Zebra Book imprint always catches my eye because they do not charge ridiculous prices on most of their books and usually the formatting is good.
Penguin is another publisher that has inconsistent formatting though it usually only needs a few tweaks before they are eReader ready.
Maybe I am just picky which is why I use Calibre to fix such issues but publisher does matter to me some before buying.
