Slides Shows - How Many Pictures?

To those of you who show your pictures as 'slide shows' - how many would you show for a 45min show?

I normally just pass around a few prints, but this time I'll be giving a 45 minute to 1 hour slide show from my recent Galapagos vacation for my co-workers. I want to avoid showing a dozen nearly identical photos of an absolutely adorable little baby frigate bird, but I also don't want to breeze through too rapidly. I don't want eyes to glaze over but I also want to provide a nice variety and show the abundance of different wildlife and environments.

So, any tips from folks on either side of what's not too much and not too little, but just right?

Thanks.

I have some experience giving lectures to various sized groups and the rule of thumb I was always taught was one slide per minute although there is a lot of room for variation. So for a 45 minute talk, about 40-60 slides; if you use the higher number have some "throwaways" at the end in case time runs short or you have a lot of questions that slow you down (which is a good thing in that it shows the audience is involved).

What's their major interest? Photography? Nature? Vacation possibilities?
Try to anticipate questions they might ask & have a few reserve slides on each topic area to illustrate your answer.

You also may want to throw together a map of the area and reference it when you're talking about specific pictures and or animals.

45 minutes is a darn long slide show.

i gave a 12.5 minute slide show, and i was able to cover tons of material...

i wasnt talking along with it, some music was playing. people aren't going to want to look at the same image for more than about 7-10 seconds in my opinion.

(none of this would apply if this was a scientific type presentation, or habitat explanation...)