I haven't read the container free baby tribe thread, so forgive me if I'm repeating what was said there.
I worked as a pediatric physical therapist before my son was born, so this an area near and dear to my heart.
Saucers, jumpers, walkers, etc. do nothing to enhance development, and can actually delay the achievement of milestones by several weeks. Essentially, to give a quick summary, standing in a saucer is not the same as actively standing while say holding onto a couch. The muscles work in a different pattern that is less desirable. This has been backed up by EMG studies, where they read the electrical output of different muscles and look at the patterns in which they are activated. Babies in saucers tend to be pitched forward onto their toes, which isn't a normal posture and can theoretically lead to tip toe walking down the road (an abnormal gait pattern). Their abdominal muscles aren't activeley engaged like they would be while actively standing. Their gluteal (butt) muscles aren't engaged the same way they would be while standing on their own. This allows them to stand with a sway-backed posture that isn't particularly healthy.
There have been excellent twin studies showing that even in typically-developing kids, the twin that used a walker walked on average 6 weeks later than the non walker using twin. Most therapists would say this can be applied to saucer use as well. Studies have shown saucers to delay sitting, crawling and walking milestones. Many parents will say their child used a saucer and walked early, but that isn't really a fair assessment, as their child may have walked even earlier if they *didn't* use one.
In a typically developing kid, it is less of a concern than a child at risk of delays (preemies, low muscle tone, etc.) However, not all parents know if their child is delayed or at risk of delays either.
The recommendation of most pediatric PTs I've known is to limit their use entirely if you can. If you insist on using one, don't use it for more than 20 mins a day, and be aware of how fast that time adds up (10 mins while you shower, 10 mins during a phone call, 30 mins while you make dinner, 10 mins while you clean up, 5 mins while you go to the bathroom...). It adds up more quickly than people realize. Also if the child shows any signs of fatigue (slouching over, slumping, leaning to one side) they should be removed before 20 mins total, and hopefully beforehand.
I know mamas need to shower and do things around the house...I can sympathize, believe me. Just keep in mind saucers are all marketing, and there is no real benefit to be had from your child using them. The manufacturers make parents feel like they really enhance development, when the opposite is true. The best "tool" for helping a child develop motor skills is floor time...supervised tummy time, just playing on the floor w/ your baby. If you need to contain them for safety, a playpen still allows them to practice their motor skills without getting into trouble if you are in the shower and can't supervise, for example.
Slings are wonderful