It's true: a wireless network will have less capacity than a 100 Mbps Ethernet LAN. However, unless you regularly move huge files around on your WLAN, or back up large disks, you aren't going to notice a difference. Your Internet connection won't be any slower, and gaming, file sharing, and printing won't be either. Depending upon how many users are on your WLAN, you should never notice a speed difference.
If you do move very large files (meaning 100+MB) around your network on a regular basis, you will notice a difference. The trade-off for the freedom and flexibility that a WLAN offers is relatively minor. WLANs are getting faster, and with the newer 802. 11g standard equipment now available, the speed difference is becoming even less noticeable.