Yesterday we were down because our host reset the servers I think. We were down for like 2 minutes, not much. The previous 2 days we were under a massive DDOS attack, but I suspect it was a paid service, we're not the type of forum that attracts many DDOS attacks, so I don't fancy spending $100+ monthly to protect us from something we hardly get.
mod_evasive is only slightly helpful aswell, we already have it installed, and we've blocked tons of attacking IP's already (around 600), depends how big the attack is on how effective these methods are. I changed our site IP as well, which didn't seem to help.
Sometimes, you can't do anything if the range of IP's that were attacking us were this big.