Well, this is an opinion, not a fact. Below you ask me to present hard statistics.
Can you at least tell me what type of abuse you think is inevitable?
Why do you want me to do it personally? You trust me more than other sources?!
OK, looks like you got me - I was guessing.
Here is <A HREF="http://www.limewire.com/index.jsp/size">the real figure - it's around 300k - 1/2 million at the moment.</A>
I guess their guess is better than mine . It's around 30 times the size of the generally accepted average horizon size.
Break is your opinion, not mine. Can you at least put forward an argument to show how it will be considered 'broken' after this change in a way that it is not 'broken' now, or to a much larger degree?
OK, the scenario you have proposed seems unlikely to me and the logic is inconsistent.

You are assuming that the 10 randomly selected hosts you have chosen are ALL searching for something widely considered inappropriate. This is already unlikely, but no doubt will happen very very occaisionally.

By definition, because this term is widely considered inappropriate, and as you say you are searching for only things widely considered legitimate, then the next ten hosts you pick up are pretty much guaranteed to accept your searches and connections.
Degree of likelihood that all clients connected to one of these 'naughty' guys are ALL connected to ALL ten of them and no one else: 0.00000000..etc..00001 %
Considered 'impossible'.
Even if the impossible happened, all that would be experienced is everyone would for 10 seconds to a minute be searching for 10 new hosts. Since the other 'hundreds or even thousands of clients' who are in your impossible scenario all connected to these 10 'naughty' hosts are all receiving pongs through the 'naughty' hosts up until the time that the 'naughty' guys perform their 'naughty' search, they will already have knowledge of a great number of 'nice' hosts, so they should find a new one without even having to visit a host cache.

Remember, the above is not going to happen.

'Naughty' searchers are going to appear rarely, one at a time.

There is a scenario where what you describe is going to happen, which will be during start up, if a very wide number adopt the strategy of 'specialising' their searches.

Let's look at it this way. I will try to describe a reasonable, but worst-case, scenario, where you the user are not searching for something considered inappropriate by most people.

Say a very high number of people think specialist searches implemented using grep is a good idea, ie search me for iso files only, or search me for mp3s only. What do you think the upper limit would be? 40% of people might think this way? I think that is a very very conservative figure.

OK, for a very back-of-the-envelope kind of figure,

n * p = t
where
n: total number of trials
p: probability that a connection will not reject you when you search
t: target number of host connections

gives
n = t/p

If we say p = 0.6 (ie 60% 'good' connections, 40% 'bad')
and you want to keep up 10 connections,
n = 10/0.6
n = 16.67

On average, a user searching for something which the specialists reject, has to talk to 17-odd hosts at startup in order to establish 10 good hosts.

This does not consider any additional host-rejection scenarios.

We can generalise the answer, by saying that t = 1
n = 1.7
You have to connect to, on average, about 1.7 times as many hosts, if there are 40% of people wanting to specialise and you search for something else. 40% is an astonishingly high proportion, and you have said yourself that you don't think this idea will take off at all.

How about if we assume 20%, still a very high figure, but perhaps a realistic high-point.
p = 0.8
n = 1/0.8
n = 1.25

Only a 25% increase in number of initial host connections required at startup.

And as I said before, this ignores the effect of hosts caching hosts who are similar to themselves. (Perhaps this effect would be insignificant anyway until you have done a few searches).

Anyway, I guess this means it might be a good idea if when rejected by a host, if you have plenty of hosts in your cache, that you delete the rejecting host from your cache, thus increasing the chances that clients cache hosts with similar search/drop criteria.
Please demonstrate how this is a bad thing. Many of the clients I have tried have constantly changing hosts, ie constantly changing horizons. So what? So the clients I search in ten minutes are different clients to the ones I searched ten minutes ago? I think this is a good thing.

I am more likely to find a result, eventually. I re-search every ten minutes, and get a different group of results. I can still download from most of the machines I located ten minutes ago, if I don't find anything. The only ones I might not be able to download from are firewalled IPs.
Maybe. Depends how badly you want them, how much time I have, and whether someone else provides an answer first.

<I>Added later: oops - confused between statistics and probability. No I do not have the statistics, but can model guessed probabilities - see later posting</I>
You should let people answer before you answer them back.
Well, you I said what I think, you said what you think, I was simply saying, people don't flood the channel if you can't add anything not already covered. That makes for a good debate too.

Nos

"We can't train that boy as a Jedi because he is too old and too
full of fear"