Access has been designed to be used more like a personal database than for corporate use. Multiple users can be supported over a workgroup alright however the total number of users (usually around 50 or so simultaneous) is small. That means Access is more useful for individual departments or the SMB (small and medium business sectors). Access also has difficulty dealing with databases larger than 2GB in size, though just to be safe one should limit usage to about 1GB.
As you scale up the size, performance becomes slow and can even reach the point of unresponsive. Use of multimedia data, even including digital camera photos, can use up this limited space very quickly. Until the 2007 version of Access, the way that images and other attachments were stored in Access databases resulted in a slowing in performance. Though the attachment field in Access 2007 takes care of that, the overall 2GB space could limit you very quickly. Many indicate that the SQL Server is a more real database, since it competes with enterprise-level databases like Oracle.
Another difficulty pointed out by many is how publishing anything other than static files is a problem with Access. It takes quite a bit of work to make data access interactive. You could use Sharepoint but that represents a significantly large investment. Many believe that the SQL in MS Access is not as robust as other databases. There's a very prevalent belief that Access is oriented towards developers rather than end users. This opinion has changed slightly with the introduction of Access 2007, but it's still there to a great extent.
This is not to say that MS Access doesn’t have its positives and for many users it has no noticeable flaws. You will notice in the above disadvantages that problems arise when MS Access is used by larger companies. For home use or small business, Access has many advantages; most notably, its familiarity to most users. It is a perfectly good system when used in its intended way.