12c database has introduced a pretty nifty Security feature which allows you to check last login time for non-sys user. e.g If I connect to scott user as below, it displays that I last logged in at Mon Jul 22 2013 09:06:07 +00:00. Time is displayed in local format (UTC in this case)

[oracle@oradbdev01]~% sqlplus scott/oracle

SQL*Plus: Release 12.1.0.1.0 Production on Mon Jul 22 09:14:25 2013

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Last Successful login time: Mon Jul 22 2013 09:06:07 +00:00

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options

If you wish to disable this feature, you can use -nologintime option

 [oracle@oradbdev01]~% sqlplus -nologintime scott/oracle

SQL*Plus: Release 12.1.0.1.0 Production on Mon Jul 22 09:16:37 2013

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options

Using connect on sqlplus will not display the last login time but will change the last login time counter