In reply to mypyrex: According to Samsung's own web site:
http://tinyurl.com/8ahbvuq the Galaxy Ace can take up to 32GB. I have a 32GB microSD card in my Defy+ and it works fine.
Beware cheap/knockoff microSD cards on eBay, even ones that are described as "genuine" can be flaky. Mine is a Memento.