It is almost impossible to know if people are sharing or not!!! Browsing is an inefficient means of finding this out. The Browse function hasn't been updated in a long time. eg: I've tried to browse someone without success. 10 mins later I browsed them & got zero results although the search results showed. 5 mins later I browsed them & got 60 results. 20 mins later or so I browsed them & got over 600 results. This has happened far too often which shows that browsing is not a definitive method of knowing if people are sharing or not. Browsing & even direct connecting can give different results on each occasion. These depend upon how much bandwidth you & them have available, & how many if any upload slots you & them have available at that time. And other factors may include local & distant traffic on the net, etc.

It is more difficult to browse someone uploading from you than someone you're downlding from. If they have the chat icon showing, there's a greater chance of a successful browse (but not guaranteed.)

Some clients are also difficult to browse if not impossible. These include Shareaza (RAZA) - generally due to lack of slots & bandwidth they offer for gnutella network, Gnucleus, ...

I don't think blocking hosts will do anyone any favors. They may well be sharing but you can't browse them at that time. It may be due to them not having chat enabled because they choose not to want to chat. At a later time you may want to downld from them (obviously you have similar interests) but since you blocked them .... just IMHO