Slugs have ruined my hostas. Should I cut the eaten leaves out ?

Yes

I don't think it will hurt the plant to cut off some of the leaves with holes. Try to get rid of the slugs. Put finely crushed egg shells around the plants. Slugs don't like sharp stuff! A bowl of cheap beer set near the base of the plant will attract slugs and they will drown.

"Don't remover the partially eaten leaves. Hostas can go dormant if they are disturbed too much. Let the leaves that are left absorb light and send nutrients into the roots for future health. " suggests Jeanne Marie on this Yahoo answers site: https://answers.yahoo.com/question/index?qid=20080515041116AA1J4tp  ; other tips and suggestions here to. I like this one because I never heard of cutting back hosta leaves, just their flowers.'Good luck!

You can prune the eaten leaves with no problems down the road.New leaves are produced all summer long.Do treat your area for the slugs.

You can definitely prune, but make sure to prevent further slug problems - mothballs and cups of beer help a lot of Hometalkers!