I always found it difficult to part with ticket stubs as they usually represent a fond memory. This doesn't mean I want them lying about all over the place though, so the diary is a nice solution. The diary is divided into two parts, the first half offers space for smaller tickets (cinema, museums, exhibitions), the second half for the larger size tickets (shows, theater).
The other reviewer has a point when he says this means that you can't put them in chronological order, but this doesn't bother me personally.