I have a Cannondale F400 that I purchased used from CL. In the last few months, I've upgraded to Avid disc brakes, a full Sram X5 drivetrain and new wheels. The bike is great, with the exception of the fork. It came with a 100mm Manitou Elite which is a crappy, low-end coil fork with little adjustability and which is very heavy, and it affects my ability to lift the front end over roots and things. I can't dial in the rebound properly, and it's the worst part on my bike.
I don't have very much to spend on a new fork, and most of the used forks I've seen on eBay in my price range (~$100) seem old, leaky, or just as crappy as the fork I have now. I was thinking about a rigid fork with disc mounts, like the Surly Instigator. It's 100mm suspension corrected, has disc mounts, is black like my current fork, and seems sturdy. Prices vary from $65-75 brand new, which is nice. It weighs about 3lbs, which will probably save me about 2lbs over my current fork, which will surely be a big improvement.
My question is how much more difficult is riding technical rooty trails on a rigid bike vs suspended? Bear in mind, the rigid fork is competing with one of the crappiest suspension forks made, so will it be noticeably more difficult to maintain control? I live in Oklahoma, so downhill is not an option, but I usually ride on very twisty single track. If anyone could share a similar experience with the transition, I would appreciate it. Who knows? If I like it, I might try out one of those rigid 29ers w/BB7s from BD!