I will also look to see what my partner has received so that i wont duplicate it. This is handy in multiple round themed swaps like Harry Potter.
I have definitely used galleries like this! I've had partners that have been in many swaps of the same theme, and it's important to me to know that I won't be sending them the same thing that they got last time. Also, not everyone deletes items from their wists after receiving them, so it's always good to see what they've received in the past.
I think the rule of not mentioning quality is a good one because it is subjective...usually the receiver can let people know about that by just posting a pic...or making a very short comment like..."I received my package"...wouldn't you be mortified if you got one of those?
I would be asking a lot of questions and apologizing and wondering how I could improve, etc. Ouch!
I've been on the receiving end of that, and it does really sting! Sometimes I'm sure I have misjudged my partner's tastes and sent something I thought they would love but they're actually like "meh." But even if you don't like what you received, it's just impolite not to say "thank you" at the very least, especially when it's obvious that some serious time/care/thought went into the craft.