I'm well aware of the different methods in replacing fonts on webpages because designers are always looking to add more tools to their design arsenal. sIFR has had limitations, but the recent methods such as cufón, typeface and Typekit have been gaining attention and I thought I'd mention some issues that are uniquely inherent about technical solutions involving 3rd party services such as Typekit.
Some immediate issues -- if their services go down:
- How will this affect the client's site?
- How will this affect the client's brand?
Relying upon any third party's services means your client's brand is susceptible to those services. I was on the Bank of Canada website when this error appeared. The service that provided BOC's date/exchange rates failed and produced an empty page with a horrible error message. Aside from a confusing message which a normal user would never understand, what should a user be thinking?