The iPhone app has a par time feature too, but like Will said, most dedicated timers won't pick up dryfire either.
I have a Pact MkIV too and have never had any problems with it. I know a couple people that have had issues with Pact though.
The MkIV is pretty awesome in what all it can do, although it is expensive. It is a chronograph (skyscreens are not included and must be purchased seperately), ballistic computer (calculating drop, etc), and a multi-featured timer. I have the HP infrared printer too for mine and that is more handy than you might think. You can print out each run and compare later. Very nice for working on the finer details of shooting. Of course it is nice when using it as a chrono too.
Another thing about the MkIV, it can actually run more than one timer at once. Let me try and explain. Say you want to work on a reload and get feedback to see if you are reloading faster than, say, a second and a half. You can set up a par time that starts after a specific shot, say the 6th shot. So you set a random delay, the timer goes off, you shoot six shots and start your reload. After the 6th shot, the par time starts counting. At a second and a half, the timer beeps and you can gauge your reload speed against that instead of having to go back through and see the actual time for the reload. All the while the main timer is still recording your shots. I admittedly haven't used this feature in a while, but it is pretty cool and I don't know of any timer that can do it.
For just a training timer, the MkIV has more features than anything out there, but many folks will never need all of them. The small CED that msshooter mentioned is really nice because of its size.
For a club timer and for running matches, I am a big fan of the Competition Electronics Pocket Pro (the original, not the "Pocket Pro II"). They are dirt simple to operate, very reliable, and have big screens that can be read at a reaonsable distance by the score keeper. I really can't think of a better timer for a club purchase. Their only downside as a training timer is it is a little more difficult to get some of the information back out of them, or just takes a few seconds longer. Once you are used to it there is really no problem.
The only timers I have ever had issues with were the yellow "R U Ready" timers, and even that was probably pretty rare.