Airport Base Station-Do g devices slow it down? Parental controls

I need to purchase a new Wi-Fi router and am looking at several but am looking at the Airport Base Station.
Most of my devices such as my Mac's all use N networking but other devices such as my Xbox 360 use g networking. When doing research on the Airport Base Station I read that when you connect G devices to the Airport Base Station it will slow down the entire network to G speed so that all your N devices really only get G speed.
Is this still an issue? Does the newer version of the Airport Base Station still do this? Has there been a firmware or hardware upgrade that solves this issue?
Also, when it comes to parental controls, does the AEBS have good parental controls? What I'm most interested in is being able to block specific websites such as Facebook so that all devices connected to the network would not be able to access Facebook. When I read up on the AEBS it appears to have some parental controls but you can't block specific websites. Is this true?

Another router I'm looking at is the Cisco Linksys E2000. A friend of mine has a E1000 and loves it. When doing research I became interested in the E2000 since it has gigabit ports.
Would g devices slow down all n devices connected to it though? What I'm wondering is if the issue with g devices is related to the AEBS or all n routers. What I like it is seems the E1000/E2000 has great parental controls for website blocking.
Thank you for your help.

It is an issue with any wifi. The newest AEBS use simultaneous dual band to take care of this. If you really need 802.11n speed - you can use 802.11n 5GHz and keep 802.11g on the 2.4GHz band thus having now slowdown. (Note that 5GHz does have a much smaller range) The AEBS also has gigabit ports.

I have not used Cisco in a long time.

Which wireless band you use really only matters in two situations.

1. Range. Wireless N has a longer range than G. If you need to roam a ways away from your router, then N has an advantage.
2. File transfer between networked drives. Transferring 100s of MB of files from one drive to another wirelessly will go faster with an N router.

Assuming you have a strong wireless connection to any particular router, wireless bands and speeds have nothing to do with internet connection speeds. Upgrading to an N router typically is not going to increase your web browsing experience. Even an old G router is capable of data transfer rates 10-20x faster then the average users high speed internet connection.

Your typical internet connection speed is 3.0-6.0Mbps. A wireless G router runs at about 55Mbps. Upgrading to a 100+MBps router is not going to get you past the 3-6 Mbps bottleneck of the typical ISP.

Actually wireless "N" as Ivan pointed out has a shorter range than "G". Wireless "N" transmitting frequency is in the 5 GHZ range which will result in faster transfer speeds but shorter range. Whereas wireless "G" broadcast frequency is 2.4 GHZ meaning slower transfer speeds but overall better range.

That's why in the TV broadcast industry, VHF signals travel farther than those of UHF. (Same reason as above.)

Actually Wireless N matters in a 3rd situation - streaming content on your internal network. So it isn't just copy/paste of large files - if you want to watch your itunes videos, or use apple tv with videos, or computer to computer HD - then 802.11n will help as well.