1. If they say that they offer 'unlimited' databases, be sure to ask them if they limit the no. of database queries on per hour basis.
2. Make sure your webhost has the latest server softwares running, especially if you need to use server side scripts such as PHP-MySQL, PERL, etc. I remember developing a site on my local machine where I used XAMPP as server and when I uploaded the site to the webhost, it didn't work at all. Reason: Because XAMPP used the latest version available then (PHP