Well, bear in mind that nobody in my campaign has teleport or scry yet, so I'm sort of testing out possibilities. I don't mind players being clever (when the wizard decides to put his fly + invisibility + spells together, that will be fine for instance... he just hasn't really thought about that yet).
It is just that the buff + scry + teleport routine is so easy to do at high levels, that the good guys would find themselves on the recieving end (since it would be stupid for capable bad guys not to do it). If one side turns up to a fight with all buff spells in place and the other hasn't... in 3e that will swing the balance widely IMO. Detect Scry isn't particularly useful since the victim will say "hey, I'm being scried" then *pop* the party arrives with several rounds worth of pre-cast spells on them! He doesn't have *time* to prepare any defences unless he has contingency to teleport himself away as soon as scrying is detected...
It isn't quite as bad as the 1e mage who used scry and then "vanish" to transport magical bombs onto his victims (now outlawed in 3e) but I want to write in some kind of limitation. Otherwise it doesn't even matter that an opponent can detect he is being scried upon, since the next second a party arrive loaded for war...
Within this limitation I believe that PC's will still be able to come up with clever tactics; it will just make a particularly lethal kind of ambush impossible.
(alternatives would be to make Scry an opposed check, which would work but would make it much, much harder to find people, to use disorientation from a teleport like Dim Door (which someone has suggested, but which I personally consider truly nerfing the power with a deus ex.), to make scry show the person clearly but everything else out of focus, for tougher teleports...)
I'm not against scry + teleport, just the arriving fully buffed portion of the ploy.