A contrarian's view
A DSLR will ///
- cost much more
- weigh far more
- take up more space in your bag
- get dust in it when you change lenses
- be a pain to clean internally (if you dare)
- require return to the manufacturer to clean (if you don't dare)
+ work in lower light *
+ have higher ISO settings **
+ take photos when you press the button ***
+ start immediately ****

* My Minolta A1 P&S focussed in lower light than the Canon 300D
** at the same ISO setting, a DSLR shoudl have less noise than a P&S
*** But my A1 also does that ... IF you pre-focus and use Manual mode
**** on the 20D certainly, not sure anout the 300 and 350

You may find you carry a DSLR less often than your P&S