I think you're talking about the evaluation version of Windows Home Server V1, which you can download through a link available on the Microsoft web site. That's not Vail, and (as the Microsoft site states) you will have to reinstall with a full
version after 30 days. I presume 30 days is chosen because it's long enough to get a taste of what the product can do for you, but not so long that you will have committed serious amounts of data to your server.
If you are talking about Vail, you can continue to use it after the 30 day activation period expires. After 30 days, activation will become annoying (very annoying) when you access the console or desktop, but all
Vail features should remain functional.
Before you decide to install Vail rather than V1, however, please consider that Vail is a beta product. This means that it's unfinished; features may change, as may hardware requirements. There may be serious bugs that have not yet been discovered. And Vail
will, if the V1 timeline holds true, not be released for many months yet. There will probably be intermediate releases which fix various issues (I would expect 2 or 3 such releases) and it's possible that Microsoft will intentionally force a "from
scratch" installation at some point, probably at the end of the beta when Vail reached the RTM milestone so they won't be left with the possibility of subtle bugs from previous versions. (Microsoft has said they're considering this elsewhere in this forum,
and I think it's a good idea.) It's even possible that there will be no support for "upgrade" installations at all during the beta, that every installation will be from scratch, for the same reason.
I'm not saying you shouldn't install Vail if you want to see what it will gain you, but I
am saying that there's a difference between using a beta product and a released version of that same product, and that difference is unlikely to be anything that will endear the product to you. :) Remember that a beta is not intended to allow
end users to evaluate the software, it's intended to find bugs and design flaws so they can be corrected for RTM.
I'm not on the WHS team, I just post a lot. :)