i would highly recomend the s45 over the 230. highly. you do have full manual control of everything. it has hundreds of options available to you. you can take amazingly great photos in any condition with it. the s230 does not have as many of these controls, therefore it is smaller, and is not near as versatile.
the s40 vs s45 is a nice upgrade. i was originally going to get the s40, until nearly everyone sold out of them. the s45 has a new digic processor which has better algorhythims to store photos, it is faster... just better.
i like the g3, but it is too big. i wanted the size of the s230, with 4mp, so i settled on the superb s45. the g3 is nice since it has a flah hot shoe, and accepts differet lenses, but i think if i want to get that high end i will get a DSLR, not a mini SLR.
my reccomendation to you- get a canon, or maybe a nikon.
check out
dpreview.com , they have an amazing mass of knowledge there. each of the three camers i have taked about are reviewed in a 16-20 page examination. there are links to other people's reviews also. if i remember correctly, all three got the best rating, highly reccomended, which i also agree with.
but ultimately, i think you would be happiest with the s45. also- you can get it for a few hundred less than the $799 or so retail. just make sure you are buying a US version with a full warranty from cannon and the entire accessory set. there are a ton of shady sellers out there. learn how to spot them before purchasing.