I have a Canon Powershot SX1 IS - if it's similar, I can tell you my experience with it.

Well, it may "feel" SLR-ish, but at 100iso you can already see noise on a 100% crop - so that sucks.  Also, it has the usual fringing going on - in high contrast situations.  Obviously the digital zoom is useless for stock.  I try to keep all my shots within 80iso (which is a nice option to have), and not too zoomed in.  I use AP for most of my shots.

What I like:

*10MP - good, but not great - and I have to size down for stock to reduce noise, etc.
*Hot shoe (makes up for the useless flash)- can use EOS flash units on it
*20x optical zoom - but remember that this is not an SLR-quality sensor
*macro setting, is at 0 cm - you will have sharpness even when 1mm from lens - I use the macro all the time, and the quality is very nice.
*Takes 4 AA batteries - convenient.  I purchased a batt charger and have 2 sets of 4 batteries that I swap - so I always have 1 more fully charged set when I go out on a shoot.
*The live viewer is huge and, unlike the pros, I use it all the time, especially when needing to take a shot low down - it tilts every which way. 
*It has continuous shooting mode, and RAW, plus RAW+JPG option (I use continuous all the time - it has saved many a bird/animal shoot)
*It has a widescreen option - I love using it for landscapes sometimes for that sweeping look. (obviously you can crop the shots yourself in editing instead.)
*It feels very substantial - solid.
*Full HD video - but sucks up your memory fast.   But, I think it will do a solid hour on an 8GB card.  (I'm considering using the video feature to take some video for stock.)
*Aperture starts at 2.8 which is nice.
*Can move the focus window around for shots where center is not the right place
*Picture review - I use it all the time to weed out shots during the shoot, and to do a focus check.
*Solid strap
*The circular dial for your thumb to change settings quickly is useful.
*Image stabilization 
*Mute mode - I love using it especially when photographing animals/birds
*Most shots turn out exactly like they appeared in the viewer, and the quality is nice enough for semi-formal stuff - in fact, most people are very pleased.  I've done weddings - candids only - engagement photos, newborn and toddler stuff, and pets.  *Quality is "good enough" to look professional to the general public - touristy stuff for example - local scenery, landscapes, architecture - in the form of cards and framed stuff.  I'm guessing this is because the color is very good, and the noise and fringing is really only obvious when zoomed in.  (photographers will see the problems though).

What I don't like:

*Price!  It cost more than an entry SLR - but I bought it because it was an all-in-one (though the quality of the shots is not worth this price).
*sucky lens cap - like all the other Powershots - doesn't fit - I use an old Tamron one I had with the spring action
*sucky lens hood - very flimsy design
*Noise at 100iso (when zoomed in 100%) and up
*Fringing is very common
*The continuous shooting is very sluggish at the highest MP - 10, with RAW+JPG turned on.
*Tons of useless features that I never use, like all the specialized settings for people that don't know how to take a picture - I'd rather have paid less and live without them.
*It doesn't take regular Canon lenses - need to get ones that fit this model exactly - and/or an adapter (Lensmate has stuff for it though - but I don't know if it's any good)
*Doesn't fit regular filters either
*Quite heavy to lug around.
*It's very easy to press the wrong button while shooting - b/c they're so sensitive
*not a CCD sensor, though it's supposed to be a better-quality CMOS
*I'm not impressed with shot quality at this price.  It's better then a P & S for shots you want to crop, and the quality is better due to the larger lens and higher MP, but it's not SLR-quality by far.
*The feeling that you "basically" have an SLR wares off fast when you try to see if your shots have the technical quality for stock.

So, there are more positives, but the negatives are more serious.  If you want it for stock you may be disappointed, though with careful editing and careful picture-taking you may be able to squeeze in okay (forget Alamy though - they don't allow it).  Keep in mind, the HD video may be another option for stock.  On the other hand, if you want to impress your friends and family, or to sell images to the public - it's a very good, though expensive, option.

I have bought lumix dmc-lx5 few weeks ago as a pocket camera and it has relatively good acceptance at micro but it's still miles behind D90. It's much more expensive than SX30 but I think that important is if there is a chance that your investment will return one fine day. I am no expert in photography, I'm "vector maker" mainly but when I take a look at sample photos from SX30 it seems that it has much more of noise - and as this camera doesn't support raw it's not that easy to remove it. But again - I am no expert.