Our version is phpBB 2.0.22. We currently occupy a whopping 19.2 MB of space for our phpBB installation. Overall, the entire site is about 100 MB.
For the first half of August, we've had 1356 unique visitors who have made 5811 visits, generating 71,881 Pages and accounting for 321726 hits. Our bandwidth usage for the first half of August is 1008.62 MB. It looks as if we are averaging around 3 GB of transfer per month for the last few months.
We also served up an addtional 62,376 pages generating 67,722 hits which used up 363.79 MB of bandwidth. This was from "non viewed traffic," traffic generated by robots, worms, or replies with special HTTP status codes.
This is actually down a bit from the previous months.