These have been appalling for quite a while. As the number of products grows, the number of database queries increases (seemingly exponentially!).
I have been investigating the causes of this, and it seems there are some issues specific to the version I use. Don't want to do a major overhaul, but I have introduced a fix which seems to have improved load times by a factor of about 3. It's not great but it is far better than it was. Please report any problems. No, not yours, with the store!!