Especially on the client side because they would love to have an intro movie that really highlighted their company before bringing the visitor to the actual website home page.
By default I suggest not creating a complete Flash website or even a Flash intro. Instead I suggest they use Flash sparing as on-page accents.
Complete Flash websites are very cumbersome to design, difficult to update and extremely expensive to have developed if quality is one of your concerns. Flash websites are also make SEO more difficult and expensive as well, usually requiring a complete HTML website also to be built. They are best suited for the websites of movies and pop stars that have the budgets to support site creation and mass media advertising to drive traffic directly.
Flash Intros are short movie type presentations that highlight the great points of a company visually before bringing you to the regular HTML website. Problems posed by intros are long load times and customer dissatisfaction proven through the high use of the "skip flash intro" button that should accommodate any site with an intro.
This article from Idaho State University, Office of Web Communications gives some good supporting arguments to the above points.
My typical suggestion of using Flash as on-page accents is well supported by this Google Webmaster Central Blog.
Try to use Flash only where it is needed. Many rich media sites such as Google's YouTube use Flash for rich media but rely on HTML for content and navigation. You can too, by limiting Flash to on-page accents and rich media, not content and navigation. In addition to making your site Googlebot-friendly, this makes you site accessible to a larger audience, including, for example, blind people using screen readers, users of old or non-standard browsers, and those on limited low-bandwidth connections such as on a cell phone or PDA. As a bonus, your visitors can use bookmarks effectively, and can email links to your pages to their friends.SEO & Flash Sites/Intros
In addition to all of the above arguments when considering the creation of an all Flash site or even just an intro you must consider that even if you get the site to rank well for desired keywords, that in doing so the site visitors that you get would never see the Flash site or intro.
So the visitors you are seeking will completely miss all of the time, energy and money that was spent on the Flash work.
Why is this so?
When someone searches to find something the search engine results do not direct the visitor to the home page (in the case of a site using an intro) or the Flash version (in the case of a full Flash site).
Take this Google search for, Constant Contact Tampa. In the results Dynamic Creations shows up (at the time of writing) on the first page with a link.
Notice however that the link directs people to the Internet Marketing page and not my homepage.
Had I had a Flash intro this visitor would never see it. Had the site been completely Flash the visitor would have not only have missed the Flash site, but would have been directed to the HTML site which likely would not have received the same design attention as the Flash version.