Hi Breezer,
That shouldn't happen, the smallest part of the system is the hose, from there the socket is slightly bigger and has a tight 90degree bend on the back to stop big objects getting into the main pipework.
The main pipe work is slightly bigger still, and all bends in the main pipework are gradually swept so that the likelihood of a blockage is reduced.
Additionally, you are advised to cut the pipes squarely and smooth them off first so that the inside of the pipe has no rough edges.
Finally they advise you put an inspection Tee in anywhere that a length of pipe has bends at both ends so that you get get a pokey stick or something in there. (I only have one such length of pipe and so have an inspection tee in the loft)
They are pretty well established in the states, so the technology is proven, I can't personally see how it could get blocked - for example a small pen won't pass the 90degree elbow behind the socket so will never get into the system, longer or thicker items get blocked the same.
And the fact that the hose is only 32mm internal, the sockets 40mm and the pipework is 48mm means that whatever gets through the hose will easily pass through the main pipework.
They do say that dust can build up in the pipework and can cause problems, but the solution is simple - vacuum up a duster or some kitchen roll from time to to clean the pipes.
The only example I can think that might block the system would be something exceptionally sticky, this could get stuck and then stick to other smaller objects. That said, and sort of as a test, I've tried vacuuming up bits of gaffer tape both flat and rolled up into a ball, and it always end up in the dust bucket, so I think it'll be fine - especially if you treat it with respect and DON'T vacuum up ridiculous things!
Finally, and I know I'm harping on a bit, but I'm just pleased with it that's all. It is easy to assume that this thing might get blocked the same way as a normal vaccum hose, but it is just so (and I mean SO) much more powerful I just can't see it happening, but I'll report back in a year or so.