ProBlogger Darren Rowse offers some tips in 7 Things to Do with your Blog when you take a Vacation.
I usually just stop blogging and give my readers (and me) a break. This does not mean that every time I don't blog for week, I'm having a vacation though...
On the other hand, I was guest-blogging for KevinMD a few months ago and it wasn't that easy but it was fun.
Another option is to hire a "blog-sitter."