Why is the World of Warcraft installation download so slow? [closed]

Have you tried disabling peer to peer download? By default, the blizzard downloader use p2p to accelerate the download, but your ISP may be throttling p2p transfer. To disable it, in the blizzard downloader, go to the View --> Preference menu and uncheck the box "Enable peer to peer".

source: http://us.blizzard.com/support/article.xml?locale=en_US&articleId=21065

The Blizzard downloader is a BitTorrent client; unfortunately, Virgin Media appear to block BitTorrent traffic. If switching Peer-to-Peer Download off doesn't work, you can try downloading from an external mirror; Blizzard have a list of sites likely to host the game files here. You'll probably also need to do this every time a new patch is released.

I've have sometimes had this problem before where the download just stops or is just crawling. My best solution is to restart the client. Otherwise try looking at Blizzards troubleshooting forums http://eu.battle.net/wow/en/forum/874936/