This has been a first for me. I usually wait for the roleplay that I am currently managing to die from inactivity or finish its objectives.

Is managing two role plays at the same time frowned upon?
Does anyone have any experience with managing more than one roleplay at the same time?

And I am referring to being the GM.

Some people are capable of managing multiple RPs at a time, some aren't. It depends on a lot of variables that are unique to you, not least of which is going to be the sheer amount of time you have available in your life to dedicate to constructing and managing your games. For myself, I have trouble managing more than one at a time because I am not an experienced GM and I also tend to construct very intricate plots with lots of details. It can be tough for me to corral my players and get them to move things forwards. Some people have an easier time because they are more experienced, or their games are not complex, or their players are more experienced and/or less troublesome to work with. I also work 60 hours per week on average and have a lot of other responsibilities in my life. Some people don't have that to worry about. You're the only one who can know what you're capable of. :)

It's only frowned upon if you suck doing it. Otherwise, give it a go and see how it works. I'd suggest creating something to keep track of the variables for each RP, in the event it doesn't quite work for ya, so you can at least refer to notes to hold you by.

Make sure you don't mix up the roleplays and post in the wrong one. (Seen that before. )

There's nothing wrong with operating 2 roleplays, or more. If you want to do that, and you are able to, then by all means do it.

It all depends on how many resources each RP demands in relation to how many you have available. In other words: Supply & Demand.

If the demand is higher than the supply, then people will be somewhat justified in complaining. If the demand is less than the supply, then few will have reason to complain (for any justified reason). Provided there's none of that mixup.

~is currently Gming 6~ Running more than one Rp is much like being a part of multiple Rps as just as an RPer. Depending on how in-depth the story line is, how many players in the Rp, how often updates need to be made, and so forth will determine if it is a good idea for you personally to host more than one. Each person is different, some can handle more than one and others cannot.

I will say that you should keep notes for each of your RP's to help save time. When you are reading posts as a Gm , making a quick note about hwat someone's characters did or something you want to make sure to address in your next update makes things a lot easier. Check your Rp's daily if you can to see if any questions have been put out there that need addressing.

Getting more than 1 off the ground at the same time is something I don't recommend but if you have 1 Rp already running well and passed that initial flood stage, then you can try a second. I stagger mine as I open them when I have spots available for hosting. Started out with one, once that was running well, started a second. If one failed, check what went wrong, make corrections, then try again.

No matter what, don't spread yourself too thin - it is better to host 1 or 2 successful Rp's than to have a stream of failing ones. If you can manage the dedication and time for more than one, go for it but don't start a second if it is going to make the first suffer. That is a quick way to kill both Rp's with one decision and why it can be frowned upon when a Gm hosts more than 1 Rp at a time.