I guess it depends on the design of the frameset. If you buy a no-name frame manufactured just for the look, then you get pretty much what you pay for. If you buy a well-designed frame, there is a real difference.

I cannot speak for the design of more than the Giant and Scott, but the purpose of those designs was to make the frame as stiff as possible without beating the rider to death. In my opinion, they achieved that. I am the first to admit that the bikes in my collection are not representative of the production bikes, as the layups are different (stiffer than the manufacturers can sell to the public), but the concept is the same.

Could there be people out there that cannot tell the difference between the bike with a tuned seat mast and a simple carbon tube? Probably, but even they may never get the chance to do an actual comparison. The reason is that the frame designed for the stock seat tube is designed with a different layup than the integrated version, so it isn't like comparing apples-to-apples.

With respect to downsides, the one that comes to mind is the same for all aero post bikes: you cannot adjust the yaw of the saddle.

One big advantage is that an integrated seat post makes it really difficult for the rider to pack his bike when traveling by airplane. This is good because then a rider will have to spend even more money to find a super huge bike case, if he can find one, and then pay the airlines even more money to fly to his destination. Airlines make more money, and those Airline CEOs making billions cann then hire more landscapers, pool boys, maids to look after their mansions...

...so really when you think about it. Integrated seat posts are good for the economy. You are helping to create jobs!

Main benefit - I never need to stop to adjust my post like some teammates after their post slips a bit or they don't think they have it exactly where it was before travelling (of course taping should alleviate this). I already had a case where I did not need to remove my seat/post, so no issue there for me. I highly recommend anyone travel with a large case anyway - I put my bike, 2 wheelsets, floor pump, etc in there. And everyone should fly Frontier with their bike, they only charge you the price of a regular bag!

Oh yeah, ISP looks cool too!

After reading all the comments, im still undecided about which weight to go.

What are the normail wieght benefits/penalties of each? And what sort of choice do you have of ISP toppers or equivelant? I am trying to achieve a light bike on a budget so buying astronomically priced seatposts is not an option.

Thanks again for the informative comments.

Generalizations about weight savings between ISP frames and standard frames is very tricky IMO as its very difficult to compare apples-apples: depends on the seat post and collar, versus the topper and how much of the ISP is cut down, etc.. As you know, seat posts and collars come in a wide range of weights and $$$. Fewer options with toppers, epsecially if you want a setback. Prices for the lightest toppers I know of, 75 - 85 gram range, run $125+ for Woodman, Tune, etc.

_________________
Wilier Cento Uno, 13.25 lbs / 6.01 kilograms
http://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=95887

so advantages
1 looks cool, and refined
2 some designs are really functional like looks elastomer e-post for comfort and in some of the ultra light weight frames it might make the frame stiffer at the the seat tube- top tube joint

disadvantages
1harder to travel with if you are tall (6'2"+)
2lower resale value

if i had a choice for the same frame in both configurations i would go for the isp version (look 586isp vs look 586 rsp) there is no wrong or right. i do believe in integration to some extent in that i do not like after market forks, i love the idea of most of a frameset made by the the least amount of companies. in theory this solution would eliminate certain compatability issues, but it also limits your choices. another point is that some of the designers have been concentrating in more than one aspect of the ride or design and i like that. by the way most isp set ups are going to be heavier than the standard seat post set up.