>  Changing your DNS records on the fly works until you run in to pesky caching
>  DNS servers.  You can crank down your TTLs in an attempt to compensate, but
>  then you have to be able to deal with the increased load from that.

Web browsers also keep their own DNS cache. Firefox's cache defaults
to only a minute.

Internet Explorer on the other hand can be a real pain. IE does not
respect the DNS TTL, and I haven't figured out what exactly it's
default timeout is (if one even exists). The only thing I can say for
sure is that IE's DNS cache expires when IE is closed. I have a user
who goes for weeks without rebooting her laptop (some users should not
be able to use suspend/hibernate....) and based on that, IE's default
DNS cache is at least multiple hours if it expires at all.

You didn't mention what kind of application you're trying to support,
but if it's a web application and your clients are using IE, things
are not going to work as you expect without some tweaks to IE. Google
for IE dns cache to find the registry changes needed, or figure out
how to get your users to restart IE when a DNS change happens.

-- 
Andrew S. Zbikowski | http://andy.zibnet.us
IT Outhouse Blog Thing | http://www.itouthouse.com