I have a ton of apps running on my old slices. A client pays monthly for the one slice and it really doesn't look like it will cover costs with the shift to their 'cloud' servers. I really don't want to have to go and reconfigure several versions of python and django and several apps. I don't want to migrate databases. I don't want to move various processes that have been running without being touched for 3-5 years.
The email doesn't give us any indication of the migration path. I don't care about your IPv6 problems or your OpenStack announcements.
Even something like domains hasn't been addressed. I use the slicehost interface to manage a dozen or so domains and their subdomains. Am I going to have to shift nameservers and reconfigure these domains?
Read their initial announcement to gain some perspective on how the acquisition was described.
"Our number one goal is to continue delivering the Slicehost experience. In fact, we hope to make it even better." http://www.slicehost.com/rackspace
It failed to say the only thing I wanted to hear: "this migration will happen automatically and you will not need to do anything".
Having failed to do that, it then failed to give me any resolution at all, just leaving a cloud of doubt and ominous phrasing about months of "dialogue". The only reason you need months of dialogue with your customer is if you are about to piss them off enormously.
I was pretty much already planning to migrate to Linode for other reasons (more RAM on the smallest server is huge), but this gives me a good reason to do it right now: months of dialogue sounds more painful than an hour or two re-setting up my server.
If you're worried about costs, Linode's price is half Slicehost's. That should make the migration time worth it.
Lesser features -- Slicehost has several kernel versions available. Rackspace Cloud does not. Slicehost control panel's UX is just much better.
In spite of all this, I've been moving as many of my customer's servers over to Rackspace for a while now. Most of them don't need the extra bandwidth you get for the slice, making Rackspace Cloud much cheaper when you add in backup images.
IPv6 is a big deal though. Everyone's going to have to touch their long-running servers sometime before the end of this year. With IPv6 Day closing in this June and the eventual migration of residential broadband to IPv6, this is one of those inevitable things that isn't going to magically go away.
I think you're confused about the implications of the IPv6 transition -- IPv4 is a subset of that address space, so existing servers will "just work" via Carrier-Grade NAT that ISPs are providing.
Some tiny percentage of the Internet is IPv6 reachable today, and it ain't all gonna change this year. The IPv4 space can't turn into a parallel ghetto Internet after all...
Dual-stack isn't the answer when you've got no IPv4 addresses left to assign.