Straight from a Shuttle America flight attendants mouth --

1 - Yes, we work both UA and DL flights (there is no uniform difference - just service and announcement differences - sometimes we screw up the annoucements, no one is freakin' perfect)

2 - We have been told by UA (who publishes what we say) NOT to make ANY mention of Continental on these flights. This is due to the scope clause / no CO code thing.

3 - There are currently no spares assigned to EWR. You're lucky if you can find a spare a/c anywhere on anyone. But yes - there are mechanics (probably contracted out) in EWR who can fix our airplanes if it's something they can do. (if it's something like not having the right part, then they're SOL)

As for the rest of your issues - not a Shuttle America problem. Take that up with UA and/or CO. We have no part in reservations, who you check in with, etc.