I guess it depends which way you are coming from....
I travel from Old Trafford tram stop to Etihad.
Before the game its not too bad as long as you are planning to arrive at the game more than 30 minutes prior to kickoff and there are no improvement works on that day (the replacement buses are an absolute waste of time). If you are planning to arrive closer to kickoff expect to miss the start due to overcrowded trams and the queues outside the ground, especially if you are South Stand as you have to include the 5 minute walk round.
After the game - Holt Town and VeloCity are both closed - and boarding at the Etihad stop can take 30-45 minutes unless you leave early (and I mean 10-15 minutes early), and even then you can wait 10-20 minutes for a tram to actually turn up. In most cases it's quicker to walk to town and get the tram home from there...but that defeats the point.
Personally I now completely avoid the tram - if I leave at the full time whistle (South Stand) and walk round to the tram and wait, it takes well over an hour for me to get to Stretford including queuing times.
If I get a lift home its 20-30 minutes (Thanks boys) or if I cycle I can be back in Stretty in 20-25 minutes)