Tyres - had a look at the Schwalbe BMX range - they look as good as anything we're riding on the trail.
Yep - I bought myself a
Mow Joe for use on my 20" uni, and it works pretty well.
I also have a 26" uni, so very direct comparison of the merits of 20" and 26" wheel sizes (granted neither has suspension, which appears it may be very important for the smaller wheels) - arguably more direct than riding a bike. I'd tried off-roading with the 20 before I got my 26, and was thinking that muni was really pretty hard - even smallish bumps were causing me problems. Was amazed at the difference the bigger wheel made - far more than I was expecting. It really does roll over bumps far better.
However to get back to the 29er debate, my understanding is that the difference in rolling is far less pronounced - it is after all only a 10% difference from 26 (bearing in mind it's really a 28.5er) compared to the 30% difference between 20 and 26. You're also at the point where the disadvantages of larger wheels start to some into play. So as mentioned above, what's best depends on what you're doing. I have to admit I've actually become convinced of the merits of a 29er for a lot of the riding I do, without even owning one!
I'm sure at some point I'll get a 29er uni at any rate (the chances of getting a 29er MTB are rather low due to my investment in 26, and decreased disposable income nowadays). Unis do make you think about wheelsize a whole lot more, as there's a whole other level of compromise going on (bigger wheel means a higher gear which could be either an advantage or a disadvantage - bigger wheel also means more stable, less manoeuvrable and higher off the ground, so harder to get on and further to fall!)
Oh, and wow at epi's little wheeled bikes. Just wow!