I play Xbox online, and PSN online and this is how i see it.
The playstation store is superiour to any of the marketplace components of Xbox Live. Not only are prices shown in real money which helps to decide how much something is actually worth but the look, feel and responsiveness of the UI is much better and easier to use.
Content purchased from PSN also has the least restricitve licencing on those products, wheras XBL licencing is restrictive beyond logical reason.
If Sony would only ship the console with a headset there would be little or no diffrence with the friends/chat systems of the 2 consoles, from what i have used however there isnt much diffrence between the two, just that you have to buy a headset for the PS3.
As for online, well it really depends on what your friends have. If all your friends have got Xbox, and you just play with randomers on your PS3, ofcourse you will enjoy your Xbox more. But to be frank the differnces are minute if any, i got some friends on Xbox, we have good fun, and ditto for the ps3.
Once you get over your Sony/Microsft fanboyisms and realise all you really want to do is play kickass games you quickly realise it makes sod all differnece wether your on XBL or PSN. The biggest difference is the cost.