I want to store one copy of every book on the bookshelves.
How many books are there in Skyrim?
How many books can fit a single "bookcase" in play homes?
Home many book cases do the houses have?

Thanks. I am trying to decide on which home I am going to invest in. I don't have enough gold to buy them all (let alone pay for the decorations).

I misspelled "Best" is that why no one helped me out?

The only house I've purchased so far in the one in Whiterun. It has two bookcases and between the two you can place about 60 or so books me thinks. I discontinued using this house though as I am now archmage of the college of Winterhold, and I much prefer the archmage's quarters. While there are around 10 bookcases, unfortunately the archmage's quarters doesn't have any bookcases you can activate so you'd have to stock them all by hand, or just pile them all into a bottomless container like I do.

I have no idea how many books are in the game but I would not be surprised if it was something between 500-1000.

Proudspire Manor or Hjerim.

I can't help too much, as at least two of the houses I should be buying are bugged, so I couldn't provide a list of bookcases per house, but suffice to say, abandon your dream until the creation kit comes out. Book cases have three shelves, with 18 books per shelf if you use the organize shelf feature instead of just manually placing books there. More could fit if you attempt manual organization, but I'll ignore that for simplicity.

According to UESP, there's 90 skill books and plus 632 other "books", which includes notes, spell tomes, journals, treasure maps, and that sort of stuff. Uncertain how many of these you consider books for your purposes. Assuming you want all those, that's about 14 bookcases. Solitude has a ton at nearly a dozen shelves, but they're either a shelf that forces you to manually place them or a smaller bookcase with 11 books and two shelves.

Proudspire would probably have the most bookcases as it's the largest house you can buy. There can be 11 books per shelf and there are 2 shelves on all the bookcases that I've seen.

As for number of books, there are:

90 skill books (5 for each skill)
4 functional books (start quests/add markers)
215 common books (although some are not so common)
90 spell tomes (I think)

for a grand total of 399 books to collect.

Thank you all. This really helps.