I just bought XSI about two weeks ago after posting a similar thread at subd.com asking for comparisons between XSI and Project Messiah. There are some free videos and courses over at
www.mesmer.com that I reccomend you download. That is why I have not been posting much lately.
The thing that has been hardest to me is the nodal render tree, it's just very different than everyone elses(Carrara, C4D, lightwave, Max). I wish they made a simpler shader ball version as an option.
I have C4d and it is great but you have to get a bundle to be able to use it (Advanced Render/Mocca) and then the price jumps alot so I have stopped upgrading.