Digital SLRs (DSLRs) usually have a larger sensor compared to compact digitals, which means better image quality (less noise and artifacts).
For example, the output from a Canon 300D SLR (6MP) is superior to the output from a Canon Pro1 compact/zoom (8MP). More megapixels doesn't always equal better quality.
If you want to take pics to put on your desktop or send to friends the difference doesn't really matter. If you want to print out posters, then it may be more relevant.
