I haven't directly observed any practical differences in ways that affect me in terms of VPS infrastructure itself, but I've found Linode's support to be significantly better and I'm willing to pay a premium for that on "sites that matter". I don't want to imply that DigitalOcean's support is bad -- it's not, but I feel they're average when compared with Linode responses.
On the other hand, my impressions may be biased since I rarely have to contact support in the first place. I'd be interested in whether or not others have had the same experience in terms of customer support.
Part of the problem is that it's very easy to compare on price, but difficult to compare on service. I think my conclusions may not be quite as valid today, because news gets around so quickly, but I think the concept is a worthwhile one to think about.
Anecdotally, I've been very happy with Linode's service: a few months ago, I had some kind of problem and things weren't booting. Panic! I sent in a support ticket, and went to their IRC channel right away. I started describing the problem, and one of the guys in the channel says "oh, I think I just answered that", and indeed, the support ticket had already been answered with real, helpful information.
My interaction with them has usually been quite positive.
One more important thing however, network stability in particular seems way better with Linode currently. I keep getting random cron errors resulting from name resolution issues on at least two data centres of DO. To counter my own last point, Linode recently had quite a lengthy network outage at Dallas, so no provider is totally immune.
Bottom line: try to build an infrastructure where you can as quickly as possible migrate/recover onto a new droplet/linode/instance, ideally across different providers.
1. DO has no private network; all traffic between your nodes occurs via your public interface. In fairness, it looks like they're working on this (http://digitalocean.uservoice.com/forums/136585-digital-ocea...).
2. Linode's NodeBalancers are super handy if you need load balancing, and don't want to run your own. There are certainly some things I wish they could do (alerting comes to mind), but they're a heck of a lot better than running my own.