Considering that you can redownload apps and if you opt into iTunes match, maybe not. But since iCloud is new and we don't know how well restore will work I think I'll keep a backup on my pc. In fact, I'm so OCD about it I also keep a backup of my pc backup on an external hard drive. I probably won't backup to my pc very often though.
For me, iCloud backups and restore is the best part of IOS5