It may just be a killer block...
It may also be that somebody is/was doing the thing where they withhold solved blocks just to screw the pool. Why would they do that? Well...swepool.net isn't that big of a pool. It does have a nice fee structure. Otherwise though it doesn't really make any sense for somebody to waste hashing power just to attack a pool. There's nothing rational that could be accomplished, so it's just dickery, if that is what is going on. And it's a very beatable thing with a little help.
In any case, the hash rate was up around 70GHash/s when all was well and normal...but people started jumping off when the block hit ~24 hours and then the difficulty changed...then people saw the rate decreasing and they left too.
Currently they are down to 11.5GHash/s.
In any case, even if you like your current pool, it should be very easy for people now to set up another .bat file, and it's good to have a few pools ready to go. It should take like two minutes to set up.
They have a nice fee structure, nice little setup overall, and they just need to break out of the death spiral they are caught in with the block that isn't being solved and the people jumping off.