If we use 192.168.1.0/24 for the RIPE meeting, and your corporate network at home uses 192.168.1.0/24 as well, most VPN clients will NOT be able to build a working connection. Try it. Given the number of attendees, the chances for address collisions with at least one participant's home network can be assumed to be near 100%.
One workaround would be to have two (vastly different) 1918 prefixes and giving people the possibility to switch (so, 2 SSID's, 2 prefixes, say 192.168.224.0/20 and 10.210.32.0/20). Chances that someone will conflict with both, are small. For better or worse, we will need to learn how to deal with this - denying these issues doesn't fix the fact that these situations will happen, without the escape of availability of public IPv4 addresses, in the near future. And, of course, if nobody puts pressure on the VPN-sellers, these issues will stick around for *years*. Geert Jan