Artwork, I usually only have problems with artwork on albums that aren't sold through the large distribution companies and I have to find them elsewhere and I wish that it would keep the artwork I paste into the track, but unfortunatley it doen't.
You can easily Embed Artwork into each Track of an Album........and iTunes will / should keep it there
I use Album Art Exchange for large 1000 by 1000 pixel (or larger) covers.......and then Copy / Paste them into the "Get Info" Dialog box of a Track or Album
Embedding the Artwork into each Track is recommended for portability between different players and systems
You can also use BlissHQ.com or Coverscout (or several others) to AUTOMATICALLY Find Albums with NO or SMALL Artwork........and Automatically Replace with 600pixel Square Artwork from Amazon & Google etc...........The Automatic is important, in that you can set it in motion on a large library at night and it will work away for several hours finding and embedding larger Artwork in your Music Library
The key point here is that iTunes will hold onto non-iTunes or "obscure" Artwork without any problem
Just so you know.........