I have had the 400d for around 2 and a half years now. I reckon around 80% of the photos I take at the moment are on Av mode, or Tv mode. There is nothing wrong with that. I find it difficult to view the metering bar on my camera.
/If/ you are using one of the preset modes, like sport, or portrait, try moving to one of these modes (Av was easiest for me, some people might prefer Tv or P). These are still automatic modes, except that you control two (well three) of the variables (in most of them, this is exposure, and Av = apertures, Tv = shutter speed, [+ISO speed] ). Almost all of your shots (well, the same proportion) will remain usable, and will teach you a little more about how the shutter speed, aperture, ISO and depth-of-field interact. Also, try and play around with the exposure setting a bit as well.
However, if you had a decent point and shoot in the past, it quite possibly had these modes as well, in which case, if you only have one lens, then there is no real difference.
The difference would be here, is in the way the photo is taken. On most point and shoots, there is either 'live view' in which case the sensor reports to the LCD screen what it can see, you look at this and decide when to press the shutter. Or (bad grammar) there is a separate view-finder. This is where the SLR comes in. It stands for Single Lens Reflex (or something similar), it basically meanst that the light you look at through the view-finder, (as the 400d doesn't have live view), is the same as that which will be presented to the sensor (ok, well, quantum theory would state that the quanta of light which have already been observed by your eye no longer exist but, ignore that). When you press the shutter release, the mirror which enabled the light to be reflected into the view-finder, moves up and out of the way, allowing the light to fall onto the sensor instead. (Ok, there is also a shutter curtain that moves out of the way, and one which moves back into the way, ensuring that a band of light, the length equal to that of the time you have selected, is presented evenly to the sensor).
Ignoring the waffle above, the main difference between a good point and shoot, and an SLR camera, is that the light waves which are entering the lens aimed at the sensor, are those that are bent and made visible to your eye. (ok, well on the 400d, you see 95% of what the sensor sees).
This means that the perspective, and the framing of what you see through the view-finder is exactly (well almost on the 400d) what the sensor will see. If it isn't viewable, then the sensor won't see it. If it is viewable, then the sensor will definitely see it. On a point-and-shoot, this may not be the case.
The other (and I suspect more obvious) difference, is that you can spend an awful lot of money buying add-ons for an SLR camera.
I have taken many landscape style shots that /I personally/ was happy with at the time. Quite frankly that is all that you need to worry about to begin with, (unless you are getting paid for them, or are into one-up-manship). I was happy with the local landscapes I took, hand-held with the 17-55mm non-IS kit lens that came with my 400d. Personally, for my landscapes I invested in a polarizer to change the way that the light falls upon the sensor, but that is a nicety which should perhaps not be at the top of your priorities unless you think it will effect the type of landscapes you are after.
I would have said don't worry about rushing into things, but you do have an ankle-biter, and they do have this tendancy of growing, so perhaps a bit of practice of portraits whilst it is still short and unable to crawl away too fast wouldn't go amiss. I don't have one myself, but apparently they are cuter when they are younger.
If you are taking portraits, then perhaps a tripod wouldn't be so bad for that either. One thing that I have found very useful, and only bought recently, was an el-cheapo infra-red remote from ebay (the real Canon one is just as good), which has a 2 second delay. You press the 2S button, the light on the front of the camera starts flashing, and you have 2 seconds to get into position. (this is also good for longer exposure landscapes, it means that the camera has stopped shaking by the time the shutter moves)
to TP 
