I use an iMac for working, and have done so for a few years now. I upgraded to 8Gb soon after I got it, and for working professionally 8h+ per day, it works really well tbh. On a typical day I am running stuff like Firefox (with quite a few tabs), Thunderbird, Twitter, Skype, Adium, XCode, Photoshop, Flash, Coda, Transmission / Cyberduck, Path Finder, a couple of terminals, RDP client, vpn client, SVN client, github client, Word, Excel, uTorrent and sometimes VMWare with an instance of windows running. I probably forgot half of it, but that's what I can think of of the top of my head. That was FINE with 8Gb.
I did, however, notice some swapping when I had lots of large open files and everything above running. Not at all unusable, only way I knew it was happening was a little bit more sluggish system when swapping between apps. I have now upgraded to 16Gb, but honestly, I have never been above ~10Gb in used memory according to iStat menus.
The point I'm trying to make is, 8Gb is enough for almost anything you need to do. Sure, if you're editing 300Mb photoshop files or editing lots of 1080p video more is better, but 8Gb is a lot. Also, even if your system does swap to disk a bit, the SSD is so blazingly fast you will probably never notice.
I'm currently working on my Air with "only" 8 Gb and a separate display, and it feels like it is running circles around my 27" i7 iMac with WD Black disk. I wouldn't turn down 16Gb ofc, but 8Gb will be enough for 99% of you guys out there.