Jup, as mentioned elsewhere, a bit too spacey.
Also I just messed around a bit with different fonts and found several sans-serif fonts way more readable than the current one.
Museo Slab is fine for headlines and short texts that need some impact but IMO it really fails when it comes down to readability here on the forums.
The reason for me is, that Museo Slab overall is a quite broad font with playful proportions. A little more line-height could help but I’d definitely recommend a more conservative choice of screen fonts for a forum.