When that happens, it could *actually* be the result of a real DDoS for once.

To explain:

When bitcoinity shows lag, this is an API request made to the Mt.Gox API, which will return the trade engine lag. This means that network-wise, the API server is reachable, but the trading engine is falling behind - so the problem is the Mt.Gox system, nothing else.

When bitcoinity does not show lag, it means that the API request made to the Mt.Gox API doesn't return lag, or it doesn't return anything because the server is not reachable. In that case, it's a likely scenario that Mt.Gox is under DDoS attack and that the server is simply unreachable.

I would guess that "the Last change: X seconds ago" would then display the amount of time that the servers haven't been reachable.