not really, happened to my old truck, nothing really happened... i do highly suggest getting it off imediatly if you ever want your engine compartment to look clean. i waited awhile and i tried everything and nother would get any of the dirt off.
It's frustrating. I clean everything under the hood and after the first rain everything looks like crap.
Don't they make liners or something that cover those gaps in the wheel wells? They might be a good idea.
I did the same thing, got mud up in the engine bay and up on the underside of the hood. I SHOULD have powerwashed it off immediately, but didn't. It now forever looks like a chocolate milk bomb went off in the engine bay. I've tried soaking it with orange clean/simple green, etc. and then powerwashing it but I think it's pretty well baked on. It won't do any damage per se, but it's not gonna look factory anymore.