If you're lagging, increase your RAM. Most of the bigger mods require at least 2GB of RAM to minecraft, and this one is no different. 99% of the time people complain about lag issues to me,especially on the server, it's because they are only using the standard half gigabyte that Minecraft automatically sets you to allot. I can typically get by playing with 1.5GB with no issues, but yeah, I'd recommend at least 2GB of RAM, maybe more if you are combining a lot of big mods.
Tl;dr- most of the people that have lag issues, it, in fact, isn't an issue with something in the mod. And I'm kind of tired of getting the bad press of it.
I have it set for 2gb and it's still laggy, but like i said im still enjoying the mod so im not complaining