I don't have an account with them, but I do believe every host oversells to a certain extent. It is the amount of effort that they put in to keep the resources green for their clients, which differentiates a host's service from the rest, and this is reflected in various aspects such as uptime, network speed, etc. These efforts can include moving clients to another server if the resources are filling up, or adding/upgrading existing hardware to increase the server's resources. Reviews do speak for themselves as well, there are plenty of positive reviews for InnoHosting on the forums.
I have a Professional plan with them and more other plans i sometimes manage for some of my clients.
2 years ago I tested "in the wild" their ability to sustain the space and band they sell. A client account was filled 9x% taking up a lot of traffic and it stayed that way 2 month i think, without no complain until my client decided to move to a bigger plan. However you may notice that despite high traffic the client website was very well optimized for not consuming CPU (a lot of pages served 100% from a cache generated by a CMS).
I don't know if they oversell or not. the question and ... the answer is disputable, overselling in fact is a very relative term, but in more than 3-4 years with them i never had performance problems.
I will try to post a innohosting review regarding all aspects of hosting with them. They have a lot of strong point, and as everybody else some weak ones.
I must also add that despite i own 2 dedicate server and a some VPS'ses i prefer to host my company site with them on a reseller account, just because their up time and stability (function like a backup solution to me for the rare moments when my dedicate servers are offline.). You must take into account for this "strange" decision i am more a programmer than a webhosting provider so sometimes i do a lot of reboots on my developing machines.
However this is a good company and a serious business. Time has proven me that.
oh and not to forget. I am talking about their US based servers. I am on server1 for example (yep i am a very old client ) and my clients are also in innohosting Los Angeles - Telecom Center location. I don't know anything about their UK servers except what i've heard from others innohosting clients (no first hand experience).
I recommend you to ask for USA location not for UK, just based on their internal forum posts. It looks like that location has the less possible problems.
warlock-m personally i consider anything else but pay what you use ... overselling. Hosting itself is a business of overselling (please don't hit me for this and read further)
We all have hosting accounts where we are paying 1 gb for example and using only ... 200mb. The rest is never used, and it's sold to other also... So, this term is very relative.
The important questions i think are if a company is able to perform well for years. How are their services. How is their uptime, support services and so on.
And the biggest question is: when you are using all you pay for a longer time what's happening? This is the big question. If it's ok, that's a nice, honest business which understand and sustain loses from here with gains from others clients.
It's very easy to "detect" insane overselling. Just look at the price. Looks too good to be true. That's probably "insane overselling" ... the rest is just "honest overselling"