They wont kick you off for ratios but they do give warnings.  If you receive (6 I think) they make you reapply.  If you get warnings then investigage more carefully but for now you are safe.  My ratio is probably about 605 as well as I try to get as much on to SS as possible as it always amazes me what sells.  I also use it as a test for the IS which I find stricter and is more difficult to upload (though I have just started using imagemanager).

What are your tyipcal rejections for?

If you're getting lots of rejections for the same reason I'd be looking into how you are doing your photos or post processing, but if they are for different reasons across your shots I'd not get to worried about it.

And as the other folks said, you don't need to worry too much unless you get some warnings from them about low acceptances..  I've heard people quote as low as 20% acceptance and they're still going strong on there.

As an asside, my acceptance ratio on SS is the highest I have at, 89%...  DT is the lowest with 66.3%.  IS is 85%, and FL 87%.   That is with the same set of images, less about 20 editorial ones I've uploaded to SS.    (Bearing in mind I don't submit much, and it's only stuff I'm 99.99% confident will get accepted.)

Cheers, Me.