A running count of Blocks in a specific region?

I need to setup a sequential ID on each block E.g. ID=Block1 and then Block2, Block3 as their displayed. I was using the visibility attribute to do this, but it doesnt seem to work the same way when I have conditions placed on the display of individual blocks. I.e it seems to display the value 1 for all blocks.

Here's what I've got:

<?php
if ( $block->region == "CONTENT"){
?>
<div class="slide" id="slide<?php print $block->visibility ?>">
  <div id="block-<?php print $block->module .'-'. $block->delta; ?>" class="clear-block block block-<?php print $block->module ?>">
    <div class="content">
      <?php if (!empty($block->subject)): ?><h2><?php print $block->subject ?></h2><?php endif;?>
      <?php print $block->content ?>
    </div>
  </div>
</div>
<?php
}
?>

I've taken a look inside the theme_blocks($region), but it doesnt give a running count of the blocks as their displayed. Any help would be appreciated.