When I can, I like to go to Catholic Mass on Saturday night, and on Sunday morning, I like to go to another church in walking distance, just to see how they do it. So far, everyone's been very accepting of a Catholic being in the premises, and they think it's really cool that I'm willing to check out other churches. No one tries to "correct" the other; people know I'm just an observer, and although I'm ready if someone mentions interest in Catholicism, they may be a little interested in me, but no one's asked me about Catholicism.
The last Protestant church I went to was an Episcopalian church where I knew the priest, and it was interesting to be part of a service so similar to a Catholic Mass, even acknowledging the Real Presence of the Eucharist. The format was the same, with the Liturgy of the Word, Liturgy of the Eucharist, and the Nicene Creed that still uses the old translation, so I was seriously thrown off.
Even though they acknowledged the Real Presence, I wasn't sure if I could take it or not, so I opted for just a blessing, and people still respected that. I'm sure this differs based on what group of people you find, but my refusal to take Anglican communion was still met with understanding that there are still differences between denominations.
The other churches I've gone to haven't been because I've known anyone, but just because they were close. And actually, the more I go to Protestant churches, the happier I am to be Catholic. The UCC and United Methodist's contemporary worship were interesting but very shallow in theology, with the UCC not acknowledging a truth to the Bible (any interpretation is fine! We don't have a group [like the Magisterium] to tell you what to think, we let everyone think their own thing!), and the contemporary worship used very little of the Bible and was based more on Christian rock songs than any deep theology. But even the very similar Episcopalian service, with the Real Presence and a liturgical structure, still had a crucial flaw; I couldn't look at the priest, and think, "Wow, this guy's a successor to the Apostles." I do that, sometimes, at Catholic Masses, becoming very aware of the deep history that runs through our beautiful Church. Nearly everything else I love about Catholicism was at the Episcopalian church, but with what is essentially a rival priesthood, as heretics like the Donatists established much earlier in Church history, I can't see it as a True Church.
