I need to weigh in on this issue as I noticed it came up on the thread "Just rode new bike". I have tried all the major types of shifter styles and I have a definite preference for down tube shifting. Brifters are a convenience, no doubt, but even Lance Armstrong uses a downtube mid 80's Dura Ace shifter for the chainrings on the left side, while admittedly does use the brifter for the rear on the right side. Why would a world champion use a dt shifter for the chainring...? Well his mechanic says it is lighter, more reliable!!!, and easier to trim. The only good reason for using the brifters are that they are more convenient and that one can shift without signaling to the rest of the peloton that you are about to make a shift. That is not an issue for me, because you can suddenly increase your cadence without any shift at all for an attack and I haven't reached Lance's level of competion either. Now I don't prefer bar end shifters because they add confusion in the area of cables and bar feel even with double crimped bars, and I feel that it makes the bike look less clean.
Do I have a preference in the area of downtube indexed or downtube friction. Well I am one of those that says that if you have a really quality rear derailleur like a mid 80's Suntour or Shimano that having friction is almost the same as indexing. Even a modern derailleur like a Shimano 105 can be so fast with friction that it's almost like indexing, especially if you have a relatively close ratio freewheel like a 13-19 or 13-23, 6 or7 speed. (Classic mid 80's bikes). I do have Suntour Accushift on two of my bikes and the shifting is perfect with no supprises no rubbing, no maintanace issues and no chain scraping the side of the next cog. The chain can be replaced with a quality chain every year or two for the unbelievably reasonable cost of $8.00 as opposed to $40 for a modern 10 speed chain which even has to be replaced 2 or 3 times for every one 6,7 or 8 speed chain. (9-10 chain is thinner, and more delicate!). Now it is true that Shimano 7 speed down tube indexing is about the best indexing that ever was and my ex had this on her mid 80's Giradano, 105 equipped bike and the shifting was absolutely faultless and has worked perfectly for almost 20 years, and sometimes without any regualar attention. Try that with brifters!
If a brifter breaks it will sometimes cost $150 to replace one and they are so delicate and complicated that this will be a frequent and unavoidable event. When 10 speed or even 9 speed shifting goes out of adjustment the effect is devastating as the sound is simply annoying. Don't even get me started on the benefits of a simple lugged steel frame over a harsh aluminum one made to be more livable with the addition of carbon fiber fork or rear triangle (carbon fiber won't last from one presidential administration to the next and is trully the disposable bike part along with brifters).
As far as friction goes, yes I am slower with my Suntour Superbe pro friction system, but more because the friction levers require more leverage than a good indexed one than the actual loss of time to make the shift. Maybe I lose a half a second for every shift when I am on my friction bike over one of my indexed bikes, and that time is real but I don't feel I give up anything to a brifter equipped bike with old fashioned indexing. Downtube shifting benefits you with increased peace of mind, reliability, improved appearance and servicability. Give a fine old steel lugged bike a chance with dt shifting and you won't wonder why so many are making the switch back to a classic ride. If it were as cheap to make a quality lugged steel bike as it is to extrude aluminum or glue up some fiber, than the peloton might still be using it today. Shimano knows that by putting brifters on all bikes today they guarantee a future replacement brifter will be made a few years from now, while the downtube crowd will still be swapping parts on Ebay decades from now, and the second owners will be getting good service from these well designed parts as will the third owner and the forth.