I brought up my beliefs casually when I first started dating my boyfriend. I would still say that this is sound advice. Testing the waters in the opening try-outs of a potential relationship is your best bet but if you're Pagan there's something it's worth remembering: there simply isn't as much readily available information about Paganism as there is about other faiths. Misconceptions and accepted stereotypes abound so it's probably going to be necessary for you to elaborate and explain more than, for example, a Christian might have to.
Provided things are plain sailing after that, you've started off well. As things progress in an inter-faith relationship there might come a point when it's obvious that expectations need to be addressed. My boyfriend doesn't follow any particular path and doesn't have set times at which to observe certain events or show reverence. His only expectation of me is that I'm honest and open about my faith and that I'm willing to share it with him without attempting to coerce him into becoming a part of it. I don't expect him to attend Pagan events or join in my celebrations of Sabbats, but I expect him to be open-minded and to give me the space to do so. At some point in the serious stages of an inter-faith relationship there might be a discussion about children and how they'll be raised. This can cause a lot of anxiety for people who believe their faith is integral to their life and want their children to have the same experience of the power of religion. For me, no such anxiety exists. I came to Paganism on my own in my own time and I would fully expect my children to begin a theological journey of sorts in their own time. I woouldn't keep my own ideas a secret from my kids. But nor would I allow myself to give them my answers before they'd asked me any questions.
It is important that both parties understand each other's spiritual paths to a decent extent. I've given my boyfriend entry level books on Paganism but he learns more from asking me questions and absorbing the answers (which is largely down to his dyslexia making focus for reading difficult). We both have an understanding of each other's childhoods and how the early ideas we were introduced to forged our paths into what they are now.
Inter-faith relationships risk either partner feeling uncomfortable, alienated or weirded out by the beliefs of the other. I touched on this issue in my first non-pagan boyfriend post. If your partner feels uncomfortable about your Tarot cards, your interest in spellcraft or the statuettes of Egyptian deities on your dresser, those things can be addressed and ironed out. Articulating what something means to you on a deeply personal level is hardly ever going to cause more harm than good when it comes to your loved one's ability to accept it. More often than not all they need is that realisation that your spiritual path is part of what makes you what you are and they'll be a big puddle of love, willing to learn more about your weird and wonderful ways. But if discomfort perseveres, you might need to accept the possibility that there's a closed-mindedness there. I mean, how often are you willing to hear, 'Those cards of yours freak me out' before you've had quite enough? Are you really willing to hide any evidence of your spirituality away to save your partner the heebie jeebies they feel when they're reminded of it?
In short, the most important ingredients for successful inter-faith romance are acceptance, openess and independence. Independence means not only being able to do what your spirituality requires of you, but also understanding that the end goal is not to convert your partner to Paganism. Since Paganism is a faith with very little evangelism, I know I'm largely teaching Pagans to suck eggs when I say that.