I'm having the same issues. I've also gone through and disabled/enabled the metadata plugins one-by-one and seem to see no difference in response. I get the "stalled" error, or after waiting for 45 seconds or more, I'll just cancel out of it.
Metadata fetches used to be pretty quick - now, painfully slow. It's almost always quicker to go directly to Amazon or B&N and do a search on the book, and then cut and paste the data to Calibre. I'm running Win7, 32 bit, Calibre 0.7.46.