Its only a valuable upgrade if you routinely move large files around on your internal network (eg. backing up machines across the network, streaming movies to devices/computers, etc). It won't benefit your internet performance, because, as others have said, even 802.11g is as fast, or faster, than home broadband connections.
That said, if you went exclusively 802.11n, you could run your router and network gear in the 5ghz band, where it would have a lot less competition for wireless spectrum from your neighbors (assuming you have lots of neighbors with wifi; my hood seems just about saturated in them). The 5ghz spectrum is also the only way to get the full performance out of 802.11n, you aren't going to get 300 mbps at 2.4 ghz.
Another factor to keep in mind is that 802.11n is backwards compatible when operating in the 2.4ghz band, but will slow down somewhat when there are 802.11g machines transmitting data. If the 802.11g machines (eg. your PS3) are off most of the time, you still get really good performance from the n devices.
The new Apple Airport Extreme is an interesting 802.11n router, as it has both 2.4ghz and 5ghz radio in it, meaning your 802.11n devices can operate on a pure n network, and your 802.11g devices have their own as well (with a bridge between them built into the router, obviously). I'm sure linksys and their ilk either have, or will have, similar dual-band devices.
Overall, right now, I don't think there is a huge rush to upgrade for most users. I wouldn't buy anything new anymore that isn't n compatible however, as its getting much more mainstream and cost effective.
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-Scott
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