Some benefits that make me like the card -
* Free checked bag for up to 9 (I think?) people on the same itinerary (otherwise $35 each bag!)
* Priority Boarding Zone 1
* $99 companion ticket (domestic coach) yearly
And, that's without even having to use the card. Also, if you go to DeltaVacations.com, for example, you can redeem towards your vacation package @ $.01/mile. As many would say, that's not the best redemption value (if you do some legwork as others have mentioned and book through a partner airline, you can do much better). But as a baseline, you're getting minimum $300 for free to use towards delta flights / vacations.
But to more specifically answer your question, redeeming the miles for actual flights can and is a nightmare. Their website sucks, and you will almost never find low fare days to anywhere worth going. They are a little better with international (specifically to Asia) where you can find some decent low-fares. You can try to call in to a reservation person, I've heard they're better.
Some things to consider before app'ing for the Gold DSM -
* This card does not earn you MQM's which count toward medallion status, which is what you need if you want upgrades and stuff
* Due to the CARD act, you cannot upgrade the account until your 13th month.
* Considering the above, I would consider the Platinum @ $150.yr AF ($55 more per year)
* The platinum version has the same companion ticket benefit, but it's free instead of $99. If this ticket will be useful to you (which it should be), then this alone makes the AF difference worth it.
I was going off memory so please verify my numbers and sorry if I got any info wrong.