My blog's on my own domain; my ISP is Bluehost. Being paranoid about my data, I take two extra steps:

(1) WordPress has an option to back up your blog (under Tools / Backup, scroll down to "Scheduled Backup"). I've set mine to email me a daily backup of the database files.

(2) Once a month I use a FTP tool to back up all the WP files, which in my case include uploaded images, WP plugins, and any customization I've done to the PHP code (not much, which makes it all the more important to back up, since I'll forget what I did).