How much companies and firms trust cloud computing providers? and do you think public cloud is a secured place?

There are many facets as far as security is concerned and a lot of those are your responsibility and the cloud provider maybe able to do little to keep it secure.

Cloud providers like Amazon have a shared responsibility model for security where the cloud infrastructure security is provided by Amazon and the application and content security is responsibility of the customer hosting on the cloud. 

With Amazon you can use something called VPC (Virtual private cloud) to restrict certain resources from outside world and only accessible to authorized users connected over a VPN.

e.g. Your application stack may have a database server, web server, load balancer and application server. The database , application and web server can be part of a private subnet thereby preventing outside access. Only the load balancer is able to access your web server. The app server can be made accessible only to web server and database server restricted to only be accessible from the application server. You may have an ERP system which is hosted inside your company and accessible to your application server over VPN.

Data security can be achieved by encrypting file system, database. Content delivery is secured using SSL.

Based on your application and compliance requirements you may need to configure additional components.

So as you see although cloud providers do provide tools and services for security your application is as secure as you architect them to be.

No - cloud is NOT a trusted storage place.

Pertaining to my domain CAD/CAM/CAE/PLM preference is to have a company hosted and confidential PDM (product data mgmt) solution.

% of the companies trust the cloud providers now specially after the compliance guarantees from the providers specially AWS and Azure.

TBH, there is not much choice for SMB's anymore due to very volatile economies and markets. Companies do not wish to spend a fortune for setting up private clouds anymore

DATA PRIVACY AT RISK as some of the companies data is highly confidential

Large cloud service providers such as Microsoft and Amazon ensure security when they offer some utility As A Service. An organization, while planning to move a service or app to cloud, may get assurance of privacy & security from the cloud provider via appropriate terms & conditions specified in Service Level Agreement. The trust of an organization on a public cloud provider is created and its level is accordingly moved up or down while enforcing security through SLA and its proper compliance by the cloud provider. However, it is the organization's call which data is to be hosted or accessed via the cloud. Usually organizations prefer to host and retain highly sensitive data and related applications within their own infrastructure while moving less sensitive apps to cloud to cut the operational costs.

It's depend on which type/company provide the cloud services.

but for big and famous companies such as Microsoft i say yes, it's secured.

Depends on what you mean by "secured". A Cloud provider may be very well protected against hackers, thus ensuring confidentiality and integrity of your information, but if it decides to discontinue a product your business relies on, then you will have a big issue of availability.