Baph

If you're downloading using an 'official' bittorrent client (eg, Azureus), then ignore the blocked port warnings.

The inbound ports are only used in bittorrent networks to allow other peers to connect to the network faster. This does affect your ratio, but only marginally. The ratio is what governs your download speed.

Basically, the tracker will announce you as a peer to any new peers, and they will attempt to connect to you, but may be refused if you block connections. However, the next time you refresh the tracker during the download (done automatically every now & again), you will connect to the peer that you refused previously (so long as your preferences permit the connection).

In short, blocked ports will slow you down, but only until the next time you refresh the tracker details, then it'll be as if you hadn't blocked ports.