There are some problems to the web version of ACT compared to the installed local version.
When using the search feature in opportunities, it doesn’t work like contacts, or companies. If you click on companies or contacts, you are able to click on more options. This doesn’t work if you have opportunities selected and click on more options. There is a work around for this but it is a lot more steps.
When adding more contacts and groups into an opportunity in the installed version it brings over the company and the contact, but in the web version it just brings over the contact.