I'm not sure I would want UGC Title elements on an ecom site, without a strong differentiation between sellers.
So a URL might look like
The Title element is one of the most important parts of a page- you should issue naming conventions and police them heavily.
There's the option of grouping several sellers on one page, under one product title (like Google Products), or you may be forced to go nuclear:
Seller| Convention-Compliant Product Title
Anyway, I'm heading way off topic here. Specifically focussed on the original question, your site is too young to worry about keyword distribution or trends. Luckily, it's youth also gives you an opportunity to quickly resolve issues WILL become a factor as your size increases.
I would strongly recommend starting a new thread for that if you need advice, as many potential contributors to that topic will no longer be viewing this thread.
. Mod's note...
UGC discussion continues here... [webmasterworld.com
[edited by: Robert_Charlton at 7:05 am (utc) on Sep 1, 2012]