You can check the rod bearings by pulling the pan. The main bearings you pretty much need to pull the crank out.

 

you can do mains without pulling the crank, just have to be VERY careful.

 

+1, you can check and replace the lower half of the main bearings real easily by just removing the main bearing cap (I think that's what it's called) and the bearings should remain on this piece as you lower it. The top will require some effort and probably be nearly impossible if you leave the timing belt and oil pump on the engine as they'll keep a lot of pressure on the top half of the bearings.

 

The problem with checking the mains with the crank in the car is that it is impossible to get all of the oil off of the upper half of the bearing because it leaks out of the oil galleys. If you measure something with oil on it and then clean it and remeasure their is a noticeable difference, especially when you need +-.0001 accuracy. Not to mention risking scratching the crank to remove them.