Sitefinity uses a In Memory cache. It is an implementation of the Enterprise Library Caching Application Block. This works fine but its a bit slack when in a multi server environment. You are effectively caching the same data on every server and thus, I think, a bit redundant. But you can create your own implementation of the CacheManger using the ICacheManager interface. I have done this and used the Azure Redis Cache, a leader in distributed cache systems.
Without doubt you should be using the built in cache features of Sitefinity. The difference is significant if you don't. One of the first tweaks is to extend the time in cache for objects. But there are a few more improvements I have found from browsing the web and I have put them together here.
I recently had a requirement for Sitefinity Ecommerce to supply free shipping for orders over a certain amount. Along with that, it needed to be turned on and off for promotions. This feature isn't supplied out of the box with Sitefinity so I had to write an extension.
Sitefinity has released 7.2 in the last few days. I found this release to be quite secretive. There was never any Road Map posted for it and as I write this the Road Map is still talking about 7.1. There is some very cool features in this release. Yet, to be honest, I am at the same time wowed and ho-humm'd about the release.
Sitefinity has good security out of the box but the one thing they can't do and you should do is secure the log on page. Even for a simple site you can get a free SSL cert or very cheap ones. They aren't high quality but they are far superior to the open plain text you are sending without them. There are also a few other steps you can take to make your site more secure.