I have to advise against these guys. Hate to do it, because the support is good, they seem like nice guys, and they are reselling SoftLayer servers, so the network is amazing.
But I've had VPS's on three different physical servers with them and they were all starved for disk IO. They take quad core servers with 16-32GB of RAM but only put two 7200 RPM IDE drives in them. A 7200 RPM IDE drive is good for about 120 I/Os per second, so if the server has 20 users you get a whopping 6 I/Os per second.
Check it out:
$ time ls -l /etc /dev/null
real 0m12.530s
user 0m0.004s
sys 0m0.046s
12.5 seconds to list a directory with ~150 files. This is from a VPS account I have with them with nothing running on it.
To be fair, most VPS hosting probably sucks just as bad.
If you use FastCGI/Rails with Dreamhost, as soon as you get any traffic they will shut down your account for "Excessive CPU Usage". I've seen it happen to a lot of sites hosted there that are linked from Reddit/Digg.
SoftLayer is indeed very good. The virtual LAN is awesome - you can even setup a PPTP VPN connection and access your virtual LAN from it.
VPN in your gateway box at home and it is almost like having the servers in the other room. They don't charge you anything for data that goes over the VPN, so you can upload/download from your server without using your bandwidth quota - it is a great for pulling off site backups.
Greenlets for lightweight concurrency, threads for preemptive concurrency and processes for parallelism / isolation.