Word is retention on IS server is maybe 72 hours and it's a revolving queue so the more people download arb stuff the lower the retention.
Very slow for uncached data. You get 5 connections. They can do maybe 3-4KB on uncached stuff. Late at night I see some 12KB/sec on uncached. Full speed on cached items though (400K/sec on 4MBit line).
The idea is for people to start caching different parts of the download so when they're done with that then the other stuff is cached already. Works very well if people work as a team rather than letting everyone else do the effort for them.
Hey, it's not a paid service so you have to live with it.
As for the news server stuff, yes, they have the same content if the newsgroup is common to them. Some might get it later than others, others will have it sooner. Does not hold for newsgroups specific to that server though. Retention of articles also depends on the news hosting company.
For IS, I do believe they pull down articles from giganews, but only when requested (i.e. uncached stuff).