No - there is definitely something wrong here. I'm not being paid for any blocks anymore
17774 2013-04-30 20:25:35 2:03:23 14233698 132 0.00000000
17775 2013-04-30 23:59:52 3:34:17 24772020 145 0.00000000
17776 2013-05-01 02:25:35 2:25:43 16453036 13 0.00000000
I have moved over to another pool, and I'm not having problems there with zero returns per block, even if my share counts are low.
The problem here is that these are fairly long blocks, and the scoring system works in such a way that shares done towards the end count more than at the beginning, but the flip to this is that with slow share submission at the end it could look like you were not sending anything and your score would be decaying faster than you were adding shares. Even if this was done with the simple calc of (your shares / total shares) * 25 * 0.98, you only be looking at 0.0002. And and average submission rate of a bit more than 1 share per minute. While slush's pool is pretty nice for most people, I don't think it is a great solution for such a low hash rate. You're just getting unlucky with score decay and too steep of a curve at the end.