...PPTP VPN: This is built into OS X, though in 10.4 it works through the peculiar 'Internet Connect' application rather than the network preferences (where I looked for it). Easy to use, requires no additional software. This style of VPN is disdained by experts for some security issues, but of course it only has to be better than nothing -- which is what everyone else at the Hotspot is using. It's the old 'park next to the better bicycle' theory...Problem is, it really slows down my browsing. Long delays for every transaction. I'll send them a note and see if they have any ideas, but I'm inclined to disable renewal of the service and try another vendor ...
Update 5/1/08: Both Witopia and a helpful commenter tell me that it's essential to use the Witopia DNS servers to get good performance. I think that's the problem, so I'll change and test. If it fixes the problem I'll amend my post title to "Use the DNS servers!". (The recommendation is down in the Witopia FAQ, I'll look over their site again but I think they could do with a bit of rework on setup documentation.)
Update 5/31/08: When I was running 10.4.11 I didn't see a way to specify a DNS address for the PPTP connection alone, and I didn't want to change my usual DNS address. With 10.5.3 it's fairly obvious how to change the DNS address for the PPTP connection alone (advanced button).
I added the DNS address from the Witopia FAQ: 18.104.22.168 Performance seems quicker, but, oddly enough, the Witopia Wiki won't open. Other sites seem fine, so perhaps the wiki is coincidentally offline. I'll test this out for a while.