I personally try to get higher. As resolutions of screens are increasing it sets me up for the future so I don't feel compelled to redo it.

Thanks Lowlander. By sheer chance that's been the size I've been saving recently for art work.

Hover over Artwork in the Artwork tab of the Properties window for a file and the tooltip will show the file dimensions. 500x500 should do in most cases.

I am currently going through a major over-haul of my music - some 14,000 tracks. I've changed songs so they're correctly named, added/removed artists etc. But when I am playing tracks on my phone some of the artwork looks pixalated. Almost as if the artwork I used originally was too small of a size. My phone shows the artwork as 6.5cm x 6.5 cm and 8.75cm diagonally. What size artwork would I need to stop having it pixalated? Also is there a way of showing what size the artowrk currently is without saving to the desktop and using photoshop?