It can be, but it really depends on how long you've been playing your Sim's family. New games with new Sims generally don't take too long to load, but the longer you play, the longer the load time due to the way the game saves world states. And the problem compounds with each of the sub-neighborhoods (World Adventures, University Life, and Into the Future) you've visited, since those world states are also saved and loaded, even if you aren't in them. Once a load time gets into the 5 to 10-minute range, I scrap my Sims (maybe save them into the bin first, if they've been particularly fun) and start over. But I know of players who have load times that run into the 30-40 minute range. Their solution is to make sure the game is paused when they save and to go do something else while everything loads.
If you're playing a relatively new Sim and getting those load times, you probably have something else going on and I'd recommend a trip to the Technical Forums for Sims 3 at http://forums.thesims.com/en_US/
