It really depend on the quality of the relationship and your agreements with her. for some couples, that would be unthinkable, for some nothing makes more sense. It's really a couple choice and a part of their habits.
The best way to know if this is the right thing for you to do as a couple is ask yourself how would you feel if she went on a vacation with her girlfriends and left you at home - before you answer "totally fine" just so you can go on your vacation, try to be totally honest.
The second question you should ask yourself is why do you prefer going with your friends, if the answer isn't "we want to spend time in strip clubs and hanging out with the local women and my girlfriend will get in the way" You should talk to her about it.
Don't inform her that you are going but ask her if that would be OK with her, she might have different fears (you don't like her anymore, you like your friends better, you are going without her so you can have sex with other women and so on) So explain what it is that you are looking for in spending the vacation without her (we want to go surfing and you are not into it, It's been a while since I got ot hang out with my friends and so on).
If you do go for it, here are some pointers that would make your return easier:
Call her a lot from your vacation. It'll make her feel less in the dark and also, loved and cared for.
Send her nice e-mails with photos from the vacation - again, seeing what you are up to, will make her feel included.
Make arrangement to spend your next vacation with her.
For extra points, and even if you are going for a weekend, send her a postcard - it's s simple gesture but getting something nice in the mail is always nice.
