What you loose in design time you gain (if not, moreso) in coding, integration and testing time. Your first few designs will take some time, and you might think it wasted, but remember your first state machine? You have to think about that up front before you coded it, and now you are probably much more efficient at putting them together because you more intmately understand state machines, and have the experience implmeneting them - getting in to OO is exactly the same. There will also be some OO concepts that you think are time wasters (like writing methods to expose private data outside a class), but once you play with it for a while and really understand why it needs to be that way, you'll never look back.
I can't disagree more - in fact, probably 75% of my OO has been little nuggets that are used by large non-OO architectures. Sure, a lot of the examples you see are of large apps, but IMHO that's no way the be-all and end-all of OO. For example, I'm currently writing a snippet of code for a partner of ours that have their own sequencer written in LabVIEW (don't go there ) - my snippet's input is a reference to the table on their FP that contains all the steps and their descriptions, and my output is a picture indicator that is a flow chart representation of the sequence. With OO, it took me about a day to set it up, without OO I don't think I could have done it in weeks. Another example is the config file VIs that come with LabVIEW - they're not a large application - they're a convenient method (pun intended) for manipulating a particular type of file.
In summary: don't think about OO as it applies to the size of a project - think about how it applies to objects. If there are elements in your system that can be thought of objects, then OO is probably the right choice, whether it be the tiniest file function or the largest application.
That is an excellent summary - nicely put Felix!
See, and now you lost me We have a bunch of OO stuff in our reuse library. What about OO means you shouldn't use it in a reuse library?