I used to own a BB Curve and with regards to the customisation of the thing, I had it for nearly 2 years and don't think I ever changed my profile/font size/whatever because all the themes I found on BB App World were awful. Personally I find the native design and look of the iPhone much much better than any profile or customisation I found on BB App World anyway. Ringtones are another thing which aren't immediately easy to change on the iPhone but again there are multiple solutions to this problem anyway.
The only thing I would suggest BBs are better with are profiles and emails. With the iPhone (mine's not jailbroken so I don't know if there is a way to change this) there are two options: silent and not silent. For me this is not too much of a problem - I have push emails turned off as I rarely get any so I'm never disturbed by the mail tone when sleeping etc. and I can still have my phone on loud in case I get any important texts/calls. I would suggest the BB is better at emails, as I said I have push e-mail turned off to save battery and because I rarely view my emails anyway, but for a while when I first got my iPhone it was turned on, and I found there was a slight delay in getting my e-mails with the iPhone, whereas they used to come through immediately on my BB. As I said, this doesn't bother me as I rarely use e-mail anyway, but for someone who had to use e-mail frequently for work (and coming from a BB too) I imagine this may be an inconvenience. Again, I'm sure there's probably a way to solve this problem anyway, as there is with most things on the iPhone, but to be honest it doesn't really bother me enough to warrant me looking for a solution anyway!
So personally the only two issues that I've ever had with the iPhone are complete non-issues. I've found the iPhone a far far better device to use than my BB. I hated having to do battery pulls, restart my phone every time I updated an app (then to start it up again took forever), and would definitely recommend that the average user make the switch!