I took the jump last week and moved my server from hmod to bukkit. Today, I've been running #186 with several plugins, 30-45 players. Lag seems to be the same if there are only 20 people on so I'm very happy with how it's performing. The server requires a lot more care to keep everyone happy but it's been great so far. What's the max connections you've seen on bukkit? I'm just curious how much it can handle.
The MineCraft forum has threads for RP servers which often have 100 people on at once with very little lag... They do require a lot of RAM though of course.
If you throw enough hardware at pretty much any software solution, you can scale it up to meet your needs. I think what you are looking for is benchmarks between the competing server mods. Something that tells you what you can expect to run given the hardware you have.
