I'm not quite a weight-weenie, but I do own and ride daily a recumbent trike/velomobile.
"... not sure how practical it is on a day in day out basis. Any experience?"
Lots! And, in general, a well-maintained velomobile is quite practical on a day-in/day-out basis. I use mine for commuting 6 miles to work twice daily in all weather comfortably. In the winter, in below-freezing temperatures, I can still ride warm with just jeans and a light sweater/pullover (cabin fills with body heat after a few minutes).
When not commuting, it's large cargo box behind the seat handles a week's groceries with no problem, or lots of beer, cola, chips, and rum for the weekend beach cook-out.
And when not doing either of those jobs, it's great fun for going fast! Top speed on flat-ground is currently limited to 46 kph (28 mph), but that's only because I'm running a low-toothed front cog (42 if I recall). I have colleagues that regularly cruise
at that speed, when they want to go fast, settling into the mid- to upper-60's on average on the flats.
Typically, a fit velomobile rider can save anywhere from 25-30% energy at the same cruising speeds as an upright "wedgie" rider - thanks to the reclined position and aerodynamic shell. And because I can cruise at a higher speed with less energy, I don't sweat so much (if at all) on the commute, which makes my colleagues happy!
2011 Steintrike Nomad with 2012 Leitra Wildcat nose fairing and Novosport tailbox. Bought the trike as a framekit, bought the tailbox second-hand, and since the Leitra velomobile builder is nearby, he walked me through the steps in making the glassfiber nose fairing myself.
Pics of production and finished ride: https://plus.google.com/photos/103124336912395863201/albums/5596262171240327505
Volunteer Aide at the Bicycle Innovation Lab http://www.bicycleinnovationlab.dk/
Support for recumbents at Copenhagen Bicycles http://copenhagenbicycles.dk
Tour guide at Recumbent Adventure! http://recumbent.greenvalues.net