Until recently I had a pbook collection of around 600 and I've read every one of those. Of course I had read more as well, from the library or borrowed from a friend or ones I had bought but given away. I've gotten rid of most of them but haven't replaced them all with ebooks as yet so my collection is much smaller now.
As for ebooks, I've got 34 and have read all but the final 3 Dresden novels. I'm saving them for my upcoming honeymoon to Fiji. I figure there will have to be some time we are so exhausted from other activities that I can think about doing some reading.
I'm very much a buy what I want to read as I am ready to read it and I keep a list of all the others that I want so I can buy them later.