There is no simple answer to the question of whether a particular wireless LAN product or technology will reach the places that you need it to reach in your home or office. Part of the reason is that every physical environment is different, with factors that mostly work to reduce a WLAN's range.
The other factor is that you can't think about distance without considering the throughput that you need at that distance. This is because the throughput (and available bandwidth) of all wireless LAN technologies declines as distances increase. Distance causes the received signal levels to decline and lower signal levels result in lower throughput. The effect is different from product to product and is not linear.
I was fortunate enough to be able to use an Azimuth ACE test system for over a year. This test system provides a controlled, repeatable RF environment free of interference, with the ability to precisely control the signal level between a wireless AP/router and client. With it, I was able to plot the throughput of numerous wireless routers and clients over their entire operating signal range. I have pulled the example below from this article, which contains a few other examples.
Figure 2 is a throughput vs. path loss (signal level) comparison of D-Link products that use Atheros wireless chipsets. The signal level starts out strong at the left side of the plot and decreases along the X axis.
The WBR-2310 [reviewed] actually uses an Atheros "Super-G" (its proprietary throughput enhancement technology) chipset, but defaults to the "Turbo" (channel bonding) part of Super G turned off. The DGL-4300 [reviewed] is also Super-G based, but defaults to having "Turbo" enabled. The DIR-625 [reviewed] is an entry-level two-antenna draft 11n router and the DIR-655 [reviewed] is D-Link's current top-of-the-line three antenna draft 11n router.
Figure 2: Downlink throughput comparison - D-Link
There are two key take-aways from the plot:
1) The throughput vs. signal level characteristic is different from product to product, with the largest changes coming from different WLAN technologies (11g vs. Super-G vs. draft 11n).
2) The maximum range (the point at which the curves end) is more similar than different from product to product, even across different WLAN technologies.
In other words, each particular combination of wireless router and client (even in a perfect RF environment) will produce different throughput at a given location. But the point at which all WLANs stop operating is more similar than different.
That last point is the most important in understanding what draft 11n products really provide. Basically, they can provide more maximum bandwidth and throughput than 11g technologies. And they generally will provide (under strong signal conditions) higher bandwidth and throughput than 11g at a given distance. But the maximum distance that draft 11n products will cover is essentially the same as that for 11g products.