I think there are MANY uses for Google Wave, but that is part of its problem. They are all very small, niche uses, which makes it hard to give a succinct description of it to someone and tell them how it could be relevant and useful to them. Also, since Wave is for coordinating with others it doesn't help to just persuade one person to try checking it out. They have to see a use for it and convince all the others on their project to give it an honest try too.
With GMail, the brand new Google Phone, etc, I just had to see that it could possibly be useful for me and try it out on my own. If it works for me, then great, I can just go ahead and use it. I can tell friends how useful they are, and since they are fairly single purpose tools they are easy to describe and simple for others to figure out if they are likely to be useful for them or not. Google Wave is much more amorphous.
Most of my friends are fairly geeky (yes, I know, quite a shocker for a slashdotter.) Back in March we started planning a group trip to Washington D.C.. We only had three weeks to plan (a friend's cousin was getting married out there and he mentioned to the rest of us just weeks in advance about it and in passing asked if any of us would like to take some days off to join in and do some sight-seeing.) Since we had limited time and couldn't all get together easily to plan we put Wave to great use. We were able to share links to points of interest, the metro system, possible places to stay; we created a roughed out itinerary that we could modify and you could click on each entry and it would show the location on the map so we could see what locations were in the vicinity to try to reduce unnecessary traveling back and forth, we put up a couple of polls for voting on what were the most and least desired to see by the group as we had to weed down a bit on what all we could do on our five day trip, and at the end of the trip we were able to share our photos with eachother. Wave allowed us to comment during lunch breaks and after work as time allowed, so even though we were unable to meet up in person or even on-line at the same time we could have group discussions about what we would like to see and do. Our trip went VERY smoothly and with the pre-planning we were able to pack in a LOT more than we ever could have otherwise on a trip like that.
My older sister just started up a new on-line magazine. She wanted to coordinate with others to figure out what format the magazine should take, be able to share and group edit the articles and layouts, have discussions about all of the physical, legal, IT logistics of getting the magazine started with the others involved, and asked me if I knew of something that could help them do all of that. I suggested Google Wave, and although the bulk of the people involved were from an English/Arts background they jumped in and found Wave to be indispensable since they all have "other" jobs while they are getting this off the ground so they do not have matching schedules or locations.
Wave can definitely start to get too unwieldy for large groups or very long running projects, so I agree with the "small projects" part, but I would definitely remove the "OSS" part.