With regards to hexing, there is also the question on what form of hexing one is talking about.
There is the deliberate act of hexing something, either through the use of Supernatural Powers like Evocation or Mana Static, or as a side effect or complication from the use of Supernatural Powers.
It is of course up to the GM's discretion, but it would seem reasonable that something which has been specifically made robustly or protected vs. interference in some way to be somewhat resistant. In the case of attempts to deliberately hex an item, then a hardened item might have a slightly greater difficulty in being damaged. The hardened item would likely not function while the hexing attempt is being made, but not nessarily be damaged/destroyed. A good example would be a Milspec GPS system being hexed would likely suddenly display ones location as being in Helsinki, Finland when under the influence of mojo, but then return to normal operation once no longer being hexed. In the case of a regular GPS unit, it would likely need replacement.
An area where some discussion and agreement from a GM would definately be needed, would be to setup a hardened/Faraday caged (and properly grounded) area where a wizard could store/use items which they did not want to get burned out. Common household items like hot water heaters and/or refrigerators come to mind here...
Incidentally, the Wizard screwing with technology thing is not restricted to electronic items, though them do seem the some sensitive. The novels routinely show Dresden's poor VW Bug breaking down, as well as less complicated devices like automatic weapons like submachine guns. In fact, one of the novels (which one currently escapes me) has a discussion between Harry and Murphy about firearms. Harry was explaining to Murphy that he preferred using a revolver since a (semi) automatic pistol could jam.
Ultimately though, it is entirely up to ones group, how they want to handle it.