I could provision a couple of EC2 servers, get Redis going on them, set up some sort of monitoring, some failover mechanism, etc. $X/month.
Or I could pay someone $Y/month to give me a Redis server I can use, and not have to care about the rest, so I can spend time worrying about things more relevant to my actual goals.
If $Y is not much more than $X, it's a very easy decision.
The whole point of redis is low latency data queries, which running on some third-party service you lose.
And again, just because I can do it myself doesn't mean I should. I came into adulthood as a sysadmin. I can take a project from bolting racks into the floor to writing front-end code, but I don't. There are better ways.
Sometimes you don't have that option (e.g. Heroku).
"yum -y install redis" then "service redis start" and it just works. I'm not sure there is an easier service to use than local redis.
Either way, I do 30K/sec queries on a single redis instance on a small instance - the performance is quite exceptional.
Edit: Someone contact me. I want to give you money!
When someone offers you "infinite scale", run.
I'd love to help you. We (RedisGreen) run extremely high-performance, dedicated Redis installations and work directly with customers to help tune their app and their installation for the best possible service.
Getting Redis up and running is easy, as has been mentioned in this thread. But the devil is in the details. Third-party vendors distinguish themselves in terms of active monitoring, quality/knowledge of support, and closed-source features (e.g. one company offers what they call "multicore Redis").
I've been running large-scale production instances of Redis since 2009, and our other team members are similarly qualified.
I'd love to help you out and give you honest recommendations on system scaling. bpo at stovepipestudios.com
A bit of googling will answer most of your redis scaling questions.