I might sound nitpicky but the language is important. “Might” or “may be” or “slower than usual” are vague and don’t offer the sender all that much information about when you’re really going to respond to them. Worse, they do a horrible job of protecting the time of the email receiver who, as the responder notes, is not in the office! Such a responder implies that, not only will the vacationer reply to the email, but they may not even miss a beat. They may be slow to respond, but they also might not.
An automatic response should include the date when you left, a reason (vacation, sick leave, a conference, etc) and, if possible, the date when you plan to come back. Thank your client for their email, promise to get back to it as soon as possible and apologize for the inconvenience. Also, it should be obvious that you’re out of office from the first sentence.

I know I’m supposed to say that I’ll have limited access to email and won’t be able to respond until I return — but that’s not true. My blackberry will be with me and I can respond if I need to. And I recognize that I’ll probably need to interrupt my vacation from time to time to deal with something urgent.
By making this information public, you have unwittingly given a hacker everything they need to complete a Business email Compromise (BEC) scam. In these BEC attacks, the hacker commits fraud by pretending to be a senior employee and will attempt to coerce the recipient into complying with a fraudulent request – such as wiring company money.