I'm perfectly alright with RP romance in and of itself, and actually enjoy it from time to time, but with a few caveats;
1.) It shouldn't be the main focus. I feel there is a difference between a "romance RP" and an "RP with romance in it". The former is creating something forced, matching two characters together and making the entire plot revolve around those two characters. The latter can be virtually any RP at all - any genre, any setup, and still open to all the creative possibilities that all other RP's enjoy - and it happens to involve romance. Nothing wrong with that at all. :P It's when an RP limits itself to just being about a romance that feels sort of... bleh. I'd prefer character romance as a side dish, not the main course.
2.) Let it happen naturally. Building off of point #1, romance RP's make a romance feel forced. You have determined from the start of the RP that characters X and Y will be together, and that just doesn't feel like a natural character progression. Instead, I feel it's better to let romances between characters happen based simply on what those characters would do. You know, kind of like how you determine everything
else a character does. Does it make sense for your character to be attracted to this other character? Are their actions, the actions of the potential partner, and the general environment of the RP lending itself to romance, allowing these two characters to fall in love the way two real people would? Then go ahead. Otherwise... if your character is doing things it doesn't make sense for them to do, then that's just not good roleplaying.
3.)
Your character is not you, and your partner's character is not your partner. This is the biggest problem that I see with romance RP's, and frankly I find it rather unsettling. When you RP, you play a character. What happens in your IC posts is called IC for a reason - it's not a reflection of what
you would do. It's a reflection of what
your character would do. And when your character's partner does things, that's
their character, and not the roleplayer themselves. Too often I see people, especially in 1x1, seem to act like they think their partner's character is actually their partner, and when their characters develop a relationship, the roleplayers develop a relationship. Honestly I find it... a bit disturbing, and probably rather unhealthy - especially if your partner isn't on the same page as you in all this. Just remember, kids: you are not your character, and RPG is not a dating site. You want to play out a romance between two fictional characters which you acknowledge are fictional characters? That's fine. You want to hook up with someone online while the two of you are both acting under the guise of characters? That's creepy, and you should probably ditch the masks and go to a real dating site where you won't confuse and disturb your potential mate when s/he realizes what's going through your mind when you RP with him/her.
But despite all these criticisms, I have no issue with two characters in a roleplay forming a natural-looking relationship. No problem at all.