I have a very short time at the moment, otherwise I would try using your code. This can help if you cannot handle it or if no one comes back with an answer using your code.
I put together a quick and dirty solution as an answer for those who wanted to show a thumbnail corresponding to the last video uploaded to Youtube by a specific user - I encoded a simple controller action and presentation that would display a thumbnail of the video that was a link to the video.
An example can be easily customized to show a certain number of videos by changing
if($i==1) break;
however, there are probably more elegant ways to do this than what I did, as I say it was quick and dirty to answer the question.
I used the Zend_Feed_Reader class instead of the Zend_Gdata_YouTube class. In the short term, this may help.
Good luck, let me know if this helped.
All the best, Dave: -D
Link to a question with my example
dkcwd source share