As with any brand, Dell has got some pros and cons. And like Maziar said, it also depends on the model. You can expect higher quality laptops from the small business latitude line as compared to those of the consumer inspiron line.
I have owned 2 Dell laptops: M170 and M1730. Both were the high end laptop at the time I bought them. The M170 was great for about a year. Then the power supply went out and I had to buy a new one. The only place I could find was Dell and it was not cheap. That new one only lasted about 6 months before it started smoking. Now that power supply is no longer being sold. I did some research on the Dell power supply thing and there are a lot of reviews about basically the same thing happening to them with whichever brand of laptop they purchase. Seems the power supply issue is something you may want to consider as a deciding factor. Also, I came across an article that there was a recall on batteries which had a possibility of exploding or catching fire. Fortunately my serial number was not in the series listed so I forgot about it.
As far as the M1730 goes:
This laptop worked great for me while on the road and had great Wi-Fi connectivity. It lasted roughly 2 years until recently I experienced another battery related issue and possible hard drive failure. Not sure if the dead battery makes it unable to access the hard drive or if they are 2 separate issues. Either way I think I am done with Dell and possibly done with laptops altogether. I can't fix them like a desktop and they fail twice as much; at least for me they do.