mattiewheels said:
I don't need anything of extremely high quality, since the first 35mm film camera I ever had was a clunker that got the job done and I still loved its quirks. If I bought, say, a $500 or $600 Canon SLR, would I get something that's a HUGE leap over their point and shoots?
I also see a 5D body on ebay for $710 with minutes to go, I suppose that's a fantastic deal there.
The three primary factors for wanting an dSLR over a P&S:
1) Larger sensor. This means optics are such that you are able to get narrower depth of field effects, leading to that look where you can get your subject in focus and have th background blur away much more readily. This is the characteristic 'look' of an SLR over a P&S. You can do it with smaller sensors, but it's harder to achieve and the effect is less pronounced given equal framing.
2) Larger sensor. This means larger pixels, which means more accurate light capturing, which means less noise, which means better lowlight capabilities.
3) Interchangeable lenses. You can get much better optics and specialised lenses.
Some fringe benefits:
Optical viewfinder that is 'through the lens'. Means you can see what you're shooting and how you're shooting. LCD can be hard to seen in daylight. Also, by holding the camera to your face, you enjoy much better stabilisation.
Depending on the models you're comparing over, much better controls and options for manual shooting. This includes focus/zoom rings, dials, configurability and so on.
Accessories such as flashes, remotes, etc are more standardised making a dSLR a little bit more extensible.
Battery life: Larger batteries combined with not using the LCD during shooting means you typically get 600-1000 shots per charge.
RAW editing. While not exclusive to dSLRs, only a few P&S cameras allow you to access the RAW image data. Most of the professional photos you've seen in magazines have been processed to get the best out of the captures, and while JPEGS can be edited, it's better to work with the RAW data rather than finalised pixel editing.
Some disadvantages:
The high end gear is very expensive (although you don't need it to see a lot of the benefits).
Size and weight. Less portable, you won't have it on you as often, and even if you do, sometimes it's a hassle to just 'whip it out'.
Movie modes, if available, are less accessible (often lack tracking focus etc.). This will change as tech improves.