In addition to the comments of deepblue above, is the simple detail that many clients permit the user to disable or disallow others from 'Browsing' them...

There are many reasons why people would wish to disallow others from browsing... One obvious one is that 56K modem users can hardly afford the bandwidth...

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Fusion for REAL!--CDex 1.51--Wackyuses--Bitzi - Check Files Before Download !--.mp3 File Name Change Problems? Try Rename-It!--Alternate PORTS--Avast- Anti-Virus--WindowWasher--IrfanView--PC Pitstop - Test your PC !--Mac OSX Troubleshooting--GO .ape ! - For 'Lossless' Audio Compression--Port :6346 - Test If It Is 'Blocked'--Cole2k Codecs--OldVersion - Newer isn't always better !
Nod32 - Free Virus Scan: Use ESET's Online Antivirus Scanner

Tomorrow's forecast:
Sunni in places, Shi'ite in others...