When trying to create a new shared photo stream, on-screen message says I have reached my limit of 100. I actually have around 50 and don't want to eliminate one to make room for a new one. iPhoto 9.4.3, Mavericks.
i suggest to upgrade to iPhoto 9.5.1. There was a very short time, when iCloud supported only 50 Shared Streams in iPhoto and Aperture. I don't remember, in which version this changed back to 100 Shared Photo Streams, either 9.4.5, or 9.5.1, but updating should fix your problem.
Yes, upgrading to the latest iPhoto 9.5.1 along with installing the latest Mavericks update 10.9.2 seems to have reset the number of shared streams. I'm now in the mid 50's with no apparant problems. Thanks!