I think some clarification is in order, just so everyone realizes what the terms state vs what may or may not be enforced.
FullTilt: disallows it while playing. The terms are spelled out in the post above, so I won't repeat.
PokerStars: disallows it ANYTIME. Even while not playing. It's on their full-time prohibited software list.
PS breaks out software that is only prohibited while playing, e.g.
Some examples of tools and services which are prohibited only while PokerStars is running are:
...a list of stuff...
and also software that is prohibited
at any time, e.g.
The following are examples of tools and services which are prohibited at all times:
...another list of stuff, including...
Table Ratings aka Poker Table Ratings
They go on to distinguish further between the two lists, and also specify the measures they take and the consequences:
Q: Why are there two lists of prohibited tools? What is the difference between them?
A: The first list details tools which are prohibited at all times. None of these tools may be used on your computer, even if not installed on the machine, and even if you do not use them in conjunction with the PokerStars client. PokerStars will take active measures to detect these tools and will take punitive action against players who have them (see 'What steps are you going to take...' below).
The second list details tools and services which may not be used in conjunction with PokerStars or while the PokerStars client software is open. We recognise that these tools have legitimate uses - perhaps for analysing your game or tracking your results - but we feel that they cross the line of what is acceptable for use during play. PokerStars will take measures to detect these tools and will issue warnings to players using them. PokerStars will also work with the developers of such tools to assist them in complying with the rules.
(all of this was just now grabbed from the PokerStars FAQ on
Prohibited Software, so it's not old info)
Now, that said, is it enforced? It used to be, and then the privacy whiners complained. Which is stupid, because it's in their TOS that they reserve the right to monitor your systems and detect illicit poker software/sites. They don't reserve the right to snoop on your passwords or your Quicken data, or anything else -- they just look for illicit software and/or site access while their client is running.
This is no different than PunkBuster and some of the other anti-cheat detection software that many PC games employ (they scan your HDD for known cheats and blacklist you from playing, even when you're aren't running the cheats), so I don't know why so many people got their panties in a bunch over this "privacy" concern. I hear it likely had a lot to do with some UK/Euro privacy laws that are extremely strict about such things, and I guess to keep from fighting those and bringing even more negative publicity to
online poker, PS at least announced "unofficially" that they won't enforce it. IIRC a PS official made that statement in a 2p2 post, where this was being discussed a year or two ago.
I always caution people, though, that because it's still in their TOS, they can "officially" choose to start enforcing it at any time. So if you're going to use it, at least be smart about how you do it. There are numerous ways to access these sites that are undetectable if you know what you're doing.
As an aside, and I think I posted about this a few days ago somewhere here, a member on DTB recently took them to task for posting links to the PTR results for their coaches. Obviously DTB does this to demonstrate the credibility and ability of their coaches. However the result was that anybody who clicks that link to be taken to PTR, has just technically violated PS TOS. Hunter Bick, DTB CEO, at first responded that they had a good relationship with PS and went on to say that PS only disallowed it while playing. After it was pointed out to him that it's actually on their "always prohibited" list, Hunter came back and acknowledged that he didn't realize that, then announced that PTR results would no longer be linked on the coach bios. Instead they will now use screenshots of the PTR pages for each coach.
So obviously DTB were concerned enough about it that they didn't want to risk running afoul of PS by encouraging people to access PTR. Which is understandable given that they had at least one PS sponsored coach on the site with a PTR link, lol.