I haven't had that problem today, but usually that means there are too many people using the forum. We aren't a very busy forum so we don't normally experience problems. The forum is on a shared server though, so maybe if another (busier) forum is causing it.
Proboards was the target of a DoS attack last month, so it could be another attack.
I've been having a different problem and I'm wondering if others have experienced it as well. Sometimes a pop-up message will appear saying that Adobe has stopped a dangerous action. I'm pretty sure it's an advertisement causing it. I use Chrome, so it might be limited to just this browser.