Hi Rich .... and John,
I don't know if you're still keeping an eye on this, but thought I should fill you in just in case.
I did a trip down the shannon from Carrick last year, as it happens I've just posted the photos on my facebook today, you're more than welcome to have a look ..
http://www.facebook.com/album.php?aid=2 ... 1c1247dd80
I also have to disagree with John ( sorry

), while the river will be busy with cruisers in July, it's big enough that they (or their wash) don't cause you much hassle, they're generally very friendly and helpful, and thankfully MOST of then have the manners and etiquette to slow down and give you a wide berth anyway.
The locks are effortless, big and roomy, all manned, and free for canoes, so you just paddle in, sit there for a while admiring the engineering and paddle out again ! - The big boats hug the walls, and there's generally a perfectly sized canoe gap down the middle, so you don't get squished.
We did the trip from Carrick to Lanesborough in 5 days, I think ? at a nice steady pace. You can see from the photos that we were both solo, so you'll cover more water in a double. It's a very scenic big river, flat and boring in places, you won't find any 2-3 on it and there are lots of various size lakes ! but enjoyable and nice pubs and restaurants along the way
We wild camped, camped at harbours with the big boats and cheated one night in a B&B. So you've got all the options there, while you can go for miles without meeting anyone, you're never TOO far from civilisation, should you need it !
Hope this is of some help, and if I can offer any more advice just shout !
The other rivers John mentioned are really nice too, and have features and moving water, I just wanted to defend the Shannon, 'cause I really enjoyed our trip last year
Grainne