You can tag any thread by subscribing to it. Once subscribed you can manage whether you want email or not from them.

You can view them by clicking the subscriptions link in the welcome panel:

http://www.rcuniverse.com/subscribe.asp

and to see which ones are updated sorted by time you can click subscribed thread activity link which is also in the welcome panel on the forum homepage.

does this sort of do what you want it to?