I wasn't entirely sure how to word this one.
What I'm getting at though is when websites/apps and so on use features such as Google Translate for translation or facebook integration for signup forms.
Would a user think less of a site/app for using these third party services?
I know that some users wouldn't even think about it, but for those who do, what is the opinion? Is using a google/facebook/twitter service ok or is it more impressive to have a bespoke system in place?
A well implemented third part service is almost unnoticeable by end users. There are many in use that do all sorts of things, a recent, common start-up business model is to provide a widget, concentrate on just that widget, then charge web masters for the use of the widget, thus reducing the amount of hardcore coding they have to do to create a website. The result of this is many different things on a website that may be third party plugins. Some examples include Disqus, Google Maps, AddThis and of course Google Analytics (and other fully hidden services).
When it comes to the third party login services users can be a bit more wary. There is much fuss about personal data and how this is used and a computer-savvy user will immediately realise that by clicking 'Facebook login' for your site they will have given Facebook knowledge of what you are logging in to but also you a certain amount of info to you from Facebook (should you choose to retrieve it). Logging in gives a very personal and obvious connection between a site and a human being, something which Google Analytics doesn't, even though it can gather almost as much data.
Looking at the other side, social login services give the user a very easy way to get into your site, a couple of clicks, via the social account of choice, which they are almost certain to be either logged into, or on a browser with their credentials saved. So while users may perceive the insecurity of their data, they may also perceive the ease with which they can use your site.
The term 'third party' is itself a bit dirty in the web world due to the association with advertising and hacking that comes around from the term 'third party cookie'. I would avoid using unless you have to, in terms and conditions for example.
In the case of a login service for your site, I would provide both options. Give the easy option via social login, but allow for a user to create an account with just your site if they want to. You should also look very carefully at the friction caused even by just asking someone to login in with Facebook - users will be most impressed if they can effortlessly achieve their goals, regardless of how they have to login.
The short answer: so long as they are unobtrusive, utilising third-party services shouldn't present negative user perception.
The long answer: it depends. The primary perception/valuation problem presented by involving third-party features is trust - if the user doesn't trust the third-party, or trusts them less than they do you, then your own trust will suffer. The key is only using external services in a way that is transparent to the user and doesn't share any user information with the third-party unless the user instigates it.
For features that have no need or possible use for user information - Google Translate, for instance - then there shouldn't be any issue using it within your site. There is little or no perception by the user that this feature of your site would be accessing their information and you can benefit from the greater audience without concern. (Which is not to say translation is the same as localization: if you're concerned at all with reaching a diverse user base your interface/app should be properly localized (l10n). Large blocks of content - articles, etc. - can be merely translated). Examples could include any number of sites that embed maps from Google or Bing, or content from YouTube or Vimeo.
For features that do need (or have a good chance of being perceived as needing) user information - such as login/signup via Google or Facebook - then they need to be clearly marked as optional (unless, of course, they are not). Users who trust the service and use it will then have the choice for their convenience, possibly increasing, not decreasing, their regard for your site. Users who don't trust the service or don't use it will then use your in-house system, costing you little or no reputation. A perfect example is StackExchange.com: when logging in or signing up, users are presented with several of the more popular services - Google, Facebook, Yahoo (and an aside explaining why OpenID is a useful thing) - but are also given the option to create an account directly with StackExchange. The third-party services that could expose the site to negative opinion are only presented as an optional convenience.
What you are thinking about is called "a mashup".
The answer to your question is :
It highly depends on the user's perception of the external service.
I don't like Facebook. This gives me a bad view on sites want me to log in via Facebook.
I like Disqus. I am incited to comment on sites using Disqus.
