Glad you like it.

Answers to questions:

1) Yes, Shareaza will requery automatically for any download which has no sources, and isn't paused. You can get it to requery for more sources even if it has some already using the "Find More Sources" command. There is no need to have any search windows open for this to operate.

2) Download source queries contain the name of the file and (if available) the SHA1 value. Other clients able to search by hash should return only exact hash matches, but non-HUGE clients may return other matches without a hash. By default Shareaza will add any sources which either have the same hash, or don't have a hash but have the same filename and same file size. You can disable this "loose" matching by turning on "Hash Integrity" in general options, which will require new sources to have the exact hash.

I don't think there are any major advantages or disadvantages personally for being an Ultrapeer -- you might get a larger horizon, but probably not by a whole lot. However being an Ultrapeer contributes to the network, so if you can (and it doesn't cost you $$) it's probably a good idea.

Sluggish performance certainly isn't normal, if it persists send an email to support@shareaza.com. The only time Shareaza might legitimately get sluggish is if you're working with a huge window of search results and sorting is going on.. which can be time consuming. The next release will have an option to turn off automatic sorting, which may assist if you often have thouands of results coming in.