I recommend you read some of the reviews on these forums for Arvixe.
I have not had one single problem with Arvixe. Video processing is super fast and always functions.
Running four sites, all with different modules and templates.
I use two shared accounts and one VPS server..
The "tools" provided are the best I have found, and support has always answered the question.
When the "cache" features were added to Dolphin recently, I simply submitted one ticket and the next day they provided memcache server address to use for my sites.
I have read of others having some problems, like high CPU loads and such. This will happen on a shared host @$5 bucks a month.
That's when a VPS server is needed. This all depends what type of community your creating and the modules used.
But most important like Magnussoft states, read all you can about the host's you find. There are many differences.