I've got an 8-man and a Supertarp with the Annex.
http://www.kifaru.net/tipi8man.htm http://www.kifaru.net/supertarp.htm http://www.kifaru.net/ptrp_annex.htm The tipi's will have a bit of condesation in them during times of high humidity. Mostly when the stove is not being used. It has been my experience that once the stoves fired up and door vent's are opened a bit, things dry up nicely. A small towel or extra tee-shirt can be used to wipe the walls down, then hung over the clothes line to dry. I've never used a ground cloth.
Kifaru also offers a liner for nearly all their shelters. The liners solve the condensation/drip problem at the 'cost' of a couple of extra pounds.
I've had my 8 for 4-5 years and have not had the urge to buy the liner yet. All of my use has been in the Northeast, mostly in the Adirondacks. I've had some 5 day trips where I set it up in the rain/snow and took it down in the rain/snow...wet the whole time...the tipi was great and the stove allowed us to start every day dry and warm.
They tipi's are pricey but they are American made, which to me, helps to justify some of the cost. They are also one of the few heated shelters that be backpacked. That covers any other 'justification' that might be necessary for myself....now the wife on the other hand... :D
As far as sizing goes...2-3 people and gear are a good fit for the 8 man...four and gear is do-able. I'm 6-0 and can move around pretty easy in the tipi.
A buddy of mine has the 12 man and that it is quite a backcountry home considering it can easily be carried by one person...stove, liner and all. I can walk all the way around the center pole with my head touching the tipi wall and cannot touch the center pole with an extended arm. Lot's of room for 4 people and gear.