As the PP said, it depends on how many days you plan to visit the parks. I personally look at it as a great value. We used it for about 10 days in mid May of 2007 and then again late April/early May of 2008 for another 10 days or so.
Current price for a 10 day w/park hopper is $287 where as an AP is $469. So if you were going to park hop and plan on visiting for either longer than 10 days each visit or plan on doing Disney back to back years, this is a great savings. In our case (using the current prices) our tickets for two trips would've been $574 vs AP $469, saving us $105 each! Not to mention ticket prices usually go up every year, so next year the 10 day is likely to cost more.
The biggest selling point for us is we really enjoyed staying off-site in a pool home. With the AP, parking is free (currently $12/day for off-site guests). So two 10 day trips within a year's time saved $240 in parking alone!
We did save some on shopping at DTD, we aren't big spenders on gifts, so our saving was minimal.
We also opted to purchase the DDE, now TIW, which saves 20% on food and beverages from most places on-site TS restaurants. A mandatory tip of 18% is added to your bill, but we looked at it as "free tipping". I realize we purchased this discount card, but we used it everywhere we ate and again used it for two trips!
I guess you need to ask yourself:
1-How many days do you plan to visit?
2-Would your touring plans include park hoppers?
3-Will you be able to vacation at Disney again before it expires?
4-Are you big shoppers?
5-Would you plan on eating at the places the AP offers the lunch discount?
6-Would you benefit from the free parking?
Other things to consider would be on-site room discount offers to AP holders. I didn't check into this, so I can't say what savings could be gained in this way.
Lastly, I would like to offer a "priceless" benefit of being an AP holder. I guess I would've been considered a commando type of tourist before becoming an AP holder. I always felt like we are paying x dollars per day so I have to be in the park from opening to closing to get my money's worth. The AP freed me from that mindset, I was able to slow down and smell the roses so to speak. Knowing you could skip some things because there was always another day to catch it, that alone was priceless!
If it works for you, go for it! Happy vacationing!