We have a domain which we are already blogging on in: blog.domain.com
There are obviously pointers to the actual website at www.domain.com. I already see it in the google index but I'm worried google will think poorly of it when we launch because it says "Under Construction" or "Coming soon".
Are there any HTTP headers or practices to help medicate this?
I would go ahead an give a description of the site you expect to be there one day, so that Google can begin getting an idea of what your site is about.
I'm basing this mostly on the widely-held belief that Google makes new sites wait a while before indexing them with competitive terms.
I never understood why anyone makes a website publically available that is "Under Construction." What exactly is the goal there? Steve over in graphic design made this lovely "Under Construction" graphic that we just don't want to waste, so we need to kick things off before the site is ready so people can see it?
...Anyway, as an answer... If you must do it, try to doll up your page as much as possible with what you want Google to think of it when it's ready, not what it is now. I don't know exactly what they do but I've heard rumors that once you get yourself on the engine's bad side, it's tough to crawl your way back up.
The Sandbox effect is totally untrue. At first the website will be marked as 'unranked', because it has been registered in the database, but not fully indexed yet. My website, NerdCulture.org, -started- with a page rank of 3. It's just a matter of knowing the tricksto get ranked. Here's a quick run down of what I've learned from being professionally trained in SEO:
1.) Avoid 'under construction' placeholder sites. Having a Top level page with no internal linking from the start will pretty much put you on Google's ignore list.
2.) In your HTML pages try to have the most minimal code to text ratio possible--this is one of the largest factors in Google's relevancy balancing that you have direct control of. Move all styling to CSS files, don't place Flash with object or embed tags--use SWFObject. This has to do with how Googlebot parses pages. It weighs your relevance by character count inside of elements to character count inside of element declarations.
3.) No tables! A table uses several lines more to accomplish the same thing as styled divs.
4.) XHTML doctypes are treated better than non-XHTML ones
5.) RSS Feeds are very valueable in search ranking.
6.) Make sure to register a sitemap with Google Webmaster's Tools and resubmit it whenever changes are made. Using a system where this is handled automatically is very beneficial. Wordpress can do this with plugins.
7.) Don't use position:absolute, if possible. Google will hold this against you as it was once commonly used to hide keyword lists behind images to cheat a high ranking.
8.) Don't make any text colors the same as any background colors. Just like the previous point, this was used for artificial ranking. Googlebot isn't smart enough to be able to tell where your text is placed in relation to it's CSS stylings, so even if the background was black and then you had black text on a white div it would be treated badly.
9.) Don't overuse meta tags! Your meta keyword block should not be more than about 150-200 characters long. If it is really long Google will assume you are just desperate to grab whatever keywords you possibly can and will have a hard time prioritizing them. It's much better to have 4-6 well-matched keywords or keyphrases.
10.) Update consistently. You can throw up several new pages every day, but it won't rank well if it's too low on content. It's better to take the time to make a well thought out page and post it when it's ready. As long as you grow the site at a relatively consistent rate (and not dissappear for half a year after daily activity, like I did with my site...) your ranking should steadily move upwards.
Follow these rules and you should have no problem ranking well if your content is good and gets your users passing the word around. It doesn't hurt to go place some links around the web yourself, but with how many links you need to rank adequately in most keywords regions you really need the users' help in link placement.
If you want to make Google happy, perhaps instead of an Under Construction site you should put AdSense for Domains content on it.
I have two "Coming Soon" websites and both appear highly in Google's Search results!
Google doesn't care if you have adsense ads in their ranking. infact you are better off not having them there at all if you have a low level of content to balance for it.
Those two "coming soon" sites are probably ranked reasonably because of being in a low-competition niche keyword region and probably have a reasonably high text-to-code ratio. If that's the case they could be ranked even better by following what I said.
My site managed to start at a page rank of 3 and place within the first 2 or 3 pages of most keywords I had targetted, despite having several million competing sites. Keywords were a very important factor in that. Trying to rank for "video games" would've just been a waste of time--the ratio of searches to competition for that phrase is far less than many of the other keywords I rank for, such as 'sin and punishment'. More targeted keywords like that are much better to bring up a small ranking. Common keyphrases are just not even worth trying for.