Where I work at we havent upgraded to Tiger yet (probably wont for while) but for those who wonder what ARD does here is an overview.
The cool stuff
It allows you to remote control users screens; interact by sharing either your screen or someone elses screen with other users screens (great if your giving a presentation or teaching). You can empty trash bins, restart, shutdown, and wake multiple machines in one step. At a glance you can tell whose machine is on, who is logged in, and what application is active in their Finder.
You drop a CD-ROM in your machine or take something off your drive and push copy it to any number of machines you can manage. You can update their ARD client software, and (most cool!) build software install packages in Package Maker (available on the developers website) and push Apple updates or do fresh installs of any OS X application on multiple machines. You can also do hardware and software detailed reporting, nice for da-boss, they like that stuff.
The stuff that needs work.
Unfortunately ARD is heavily dependant on Multicast and there is no unicast option available in 2.1. I say unfortunately because at least where I work its $100,000 in firmware upgrades on our Foundry core switches to enable this feature talk about retarded licensing! (Believe it or not its still less than Ciscos even worse) so thats not happening for a bit. This means you cant wake machines remotely in other subnets other than your ARD server is in (if you have a plight like mine). To offset some of the pain though you can just not let your Macs go to sleep, being UNIX is the engine for OS X this is no big deal UNIX prefers this anyways. From time to time using ARD can cause your Mac to freeze up completely and doesnt always play nice, but that is an occasional issue.
How it compares to other stuff out there
For $600.00 to get unlimited licenses, very sweet indeed. ARD remote control is a little better than VNC in performance but depending on which VNC distribution you use the difference varies. Microsofts Terminal Services or Remote Desktop sharing has the best performance when taking over someone elses desktop (less latency, faster redraw, and you can set level and type of encryption) but Citrix who is behind their product has done a very good job of making that product work.
If you were to compare ARD with what Microsofts solution is it would be a cross between Microsofts Remote Desktop and SMS server, SMS adds many more features and is more scalable than ARD but is also much much more expensive on the enterprise too.
Well time to go refill the morning cup-o-joe.