Hello,
Thanks for your interest in Linode.
1) Currently all bandwidth is accounted for, but we're working on support for private back-end networks between Linodes within the same datacenter that will remove this limitation.
2) In my opinion, I think all three data centers are great. Atlanta does block some ports, but the only one we ever get complaints about is IRC (port 6667). Most IRC networks have alternate ports you can connect to (8000 for freenode, 6668 for oftc).
IPs to test latency, and files to download:
http://www.linode.com/forums/viewtopic.php?t=2636
3) Larger plans do not get more IO tokens -- the reason for this is that the token IO limiter is only there as an "emergency brake" for runaway Linodes. You should not hit the limiter under normal operation.
4) We've got Xen beta boxes in all three datacenters
5) You can compile anything on your Linode, including kernels, but you can only use the kernels we provide. The kernels we provide have all of the useful stuff enabled (tuntap, a lot of the iptable stuff, etc). Under Xen, you can compile your own modules.
6) Since UML is a (set of) processes on the host, the host can indeed swap them out, however, we never oversell. The full amount of RAM allocated to your Linode *is* physical RAM and will never be swapped out.
Hope that helps,
-Chris