Your solution wasn’t for me, I think we had different problems. The 2.5 update fails to create (at least in my case) an index for the comment_date_gmt column in wp_comments. I found the answer here.
Basically load up phpMyAdmin, select your wordpress database, click on wp_comments and find the column “comment_date_gmt”. Click on the index button in that column (in phpMyAdmin it looks like a lightening bolt).