Back in 2004, so even longer ago that the start of this thread I ultrasealed the Bonnevilles tyres as two up with soft luggage (waiting for the rack to be made) we were short of space. I put the gloop in on the Thursdays night and on the next Tuesday we were less than a thousand miles away getting a puncture fixed

The good bit: The nail had made about a dozen pin ***** holes that the goo had sealed.

The bad bit: The nail, working in the tyre then managed to hit the seam of the tube and make a V-shaped cut resulting in a complete loss of air.

We came out of the Bayeaux Tapestry to find a very sad looking bike sat on the rim. In France this was no problem, a mad Polish tyre fitter gave me a choice of a new tube (Branded or Chinese Sir?) or a patch via some pretty crude sign language while his chain smoking Gallic boss made us coffee and chatted up my wife. We were back on the road in an hour for under twenty quid. This proves:

a) France is more civilised than the UK.
b) Ultraseal mostly contained, only causes repair issues to lazy cockney rip off merchants (like a certain Surbiton Honda dealer of my experience) who'll give you the old "Nah mite, the 'ole tyres ****ed" routine followed by "Sorry Mite, can't even touch it fer a week, it's them black rahnd tyres, can't get 'em for love or loads-a-money".
c) Ultraseal can work but at some point the dam breaks. Imagine if the V-cut had opened up at auto-route speeds .

IMHO, if you use the gloop put it in only after you find and remove the cause of the puncture. If you can carry and use a patch/plug kit (Which I do now the luggage is sorted), that's still a better solution.

Edit to add: My whole pack of long distance tyre stuff (Tubes, levers, patch kit, compressor) can't actually be much bigger than the bottle of gunge. I image a leaking bottle of Ultrasteal would ruin your day?

Andy