Reading through all these differences in practices and organisations has made me appreciate my own church a lot more. We have three regular bands, each with a regular sound engineer. Practices are in the week before, Tuesday or Friday depending on the band, and on Sunday morning there is a final run through of whatever length is needed, stopping half an hour before the service starts. Newbies, e.g. me, are encouraged to sit in on rehearsals and gain confidence with a band before playing live.
We still change keys during rehearsal, repeat verses in the service at no notice, sometimes forget who is playing this week and so on, but there is an understanding from everyone that if we're going to do this we should do it right.
Best of all we have a congregation who do like to sing up, appreciate good music, and are very forgiving and occasionally amused when something goes horribly wrong.