Limits aren't exactly bad. In some cases, they keep a RP going. Personally, I agree with Ariamis. A GM should state their rules and expectations regarding posting, then enforce those rules. I've been in two RPs that have lasted for quite sometime, one has been alive for more than a year and the other almost a year, and both have strict posting rules. Those who were inactive, or those who slowed the RP down were kicked out. Lack of posting can lead to a lack of motivation and sometimes when things go quiet people lose inspiration. I've seen several RPs go to their grave because of a lack of posting. Things went quiet and people assumed it was dead and left. If the IC is going to be quiet or slow for sometime, it would help to keep the OOC active and show the players that the RP is still alive and kicking.

Personally, I'm all for limits, but perhaps that's because I don't want to wait an entire month for a single reply. However, it depends since other RPs do fine with a more relaxed pace. Still, I agree with Ariamis, post down your rules and expectations, that way you'll find a group of people who meet your RPing needs. Some people prefer faster RPs and some people are more patient than others, so it's a matter of finding players who are looking for the same things that you're looking for.

And Evan is definitely right, being friends with your fellow RPers helps a ton. It's easier to RP with them and iron out the kinks when you feel comfortable with them. Get to know them, have a laugh with them, and remember communicate with them. If there's something you don't like or something that needs to be discussed then talk about it on the OOC. Also, if someone drops off the face of the planet don't be afraid to give them a little kick through PM. Communication does a RP wonders.