Reasons not to use an auto-incrementing number for a primary key

Question

I\'m currently working on someone else\'s database where the primary keys are generated via a lookup table which contains a list of table names and the last primary key used

Answer 1

from CodingHorror:

GUID Pros

• Unique across every table, every database, every server
• Allows easy merging of records from different databases
• Allows easy distribution of databases across multiple servers
• You can generate IDs anywhere, instead of having to roundtrip to the database
• Most replication scenarios require GUID columns anyway

GUID Cons

• It is a whopping 4 times larger than the traditional 4-byte index value; this can have serious performance and storage implications if you're not careful
• Cumbersome to debug (where userid='{BAE7DF4-DDF-3RG-5TY3E3RF456AS10}')
• The generated GUIDs should be partially sequential for best performance (eg, newsequentialid() on SQL 2005) and to enable use of clustered indexes

The article provides a lot of good external links on making the decision on GUID vs. Auto Increment. If I can, I go with GUID.