There are going to be players that are going to get very frustrated with the ballkids in the next few months. Toweling off is definitely not a valid excuse for taking more than 25 seconds. That will be one of the negatives of the new rule, I'm afraid. I just hope that none of the players receive a time violation on a big point, and have to hit a second serve, and then turn around and rip into a ball kid verbally for taking too long to get them their precious towel.
Another negative, is that if there is a rule question, or a dispute about something, the chair umpire will have a little bit of discretion with time to answer a question or 2 before going back to the clock. Once the players catch onto that, there may be some more ridiculous arguments or discussions over stupid things, which is something that has drastically improved with the addition of Hawkeye.
While there are some people that use ridiculous Hawkeye challenges with the intent of buying more time, there are a lot of players that go through several matches without using a challenge that aren't when they legitimately thought the call was wrong. Once the players realize that the 25 seconds doesn't start until the OUT/IN image is revealed, there may be several more wasted challenges.
While I have never been a fan of the "shot clock" idea, I do think that if the chair umpire's discretion is taken out of the equation, and time violations will be given each and every time 25 seconds is exceeded, I do think it may be a good idea to have one, because it's tough to judge when you are actually playing the difference between 22 and 27 seconds. It may save several time violations if a player looks up and says, "I'm at 20, get to the line and serve."
Another thing to remember is that the umpire controls the clock. The time clock on the PDA starts as soon as the umpire enters the point into the PDA. That does not happen EXACTLY when the point ends. The chair umpire's technique is to check the point loser at the end of the point to make sure he's not going to chuck a racket, or launch a ball, or do some other code violation. THerefore, the clock may not start for 1-3 seconds after the point ends. So, when the TV networks put that image on the bottom of the screen that shows the time since the last point, it may show 26-28 seconds, but the umpire's clock may say 22-25.
There is no absolutely perfect way to do this. There will be positives and negatives to just about everything that they can come up with. I do think that losing a serve makes it more fan friendly, better on the players, and more enforceable for the umpires than a loss of point.
Also, the players have been being warned about this new change for the last couple of monts of last season. It shouldn't be a surprise to them.
Of course, at the Australian Open, it will be 20 seconds (not 25), and it will be up to the umpire's discretion again. That is the main problem I have. They just need to get on the same page. Brad Gilbert and John McEnroe are going to be broadcasting at the Aussie Open blasting the umpires for not following the new rule, because I can guarantee you that they will have no idea (as they are usually clueless about the rules) that it's different.