I bought an SL3 with a skirt but have never brought it along. I love my SL3 but don't want a floor (because of my constantly wet dog) so I thought I'd pick the one with the net up for use when I thought mosquitoes might be bad. Generally, they aren't that bad here and I try to camp in a high, dry, breezy spot whenever I can. I have certainly been chased inside by mosquitoes but they don't come in under the bottom much. And those that do fly up and hang around the vent. So mine has worked fine. Right after I bought the one with the net, I was hiking past someone camped in a meadow close to a stream in a Supermid and there were plenty of mosquitoes. I went over to talk to them and they said the same thing. The mosquitoes didn't really come into it.
To Justin's question, this one is sewn own. I'd think the only practical way to have it removable would be to use velcro. The skirt on mine already adds about 8 oz. Adding 28 feet (based on Duomid's specs) of velcro is going to push the weight up considerably higher. I just weighed some velcro and it's close to .25 oz/ft (might be lighter velcro options, I don't know). That would add 7 oz.
I don't see why the skirt wouldn't provide complete mosquito protection but a removable skirt doesn't seem like a good solution from a weight perspective unless you really don't want a floor so you don't want an inner. Otherwise the inner gives you more options. If you primarily hike where mosquitoes are a significant problem so you always want the protection, a skirt may work just fine and be lighter than the tarp/inner combo.
