Your host count only shows the Ultrapeers you have seen yet. Other non-LimeWire clients and LimeWire leaf-nodes don't appear in that statistics. You can multiply that number by 50 to be able to make a safe guess.

The longer you are running LimeWire, the more hosts, you statistics might show, since your client will not become aware of any Ultrapeer that does not send a certain message to the network and the longer you stay online, the more likely the Ultrapeer is to send the message.

After running LimeWire an hour or so, my host count is usually between 500 and 1500. This host count has no direct impact on the number of hosts you reach with a search, however.