We have got dozens of applications running on Informix Ver 7.x &
9.x on Solaris for several years successfully.
Now we are planning to upgrade all these installations to Ver 10.

What are the key things that we have to keep in mind from development
perspective (code perspective) in order to successfully perform this
task ?
I know few things like
(1) We could have issues with new reserved words (that got added in
various releases)
(2) The limit on # of varchar columns in a table has been reduced
(3) DBAs have to revisit all the config params and tune them properly
after the upgrade.

Any other big things / obvious things that we have to worry about ?
I am more interested in knowing the risks that we are taking (rather
than benefits we might get) by disturbing the stable systems with
this upgrade plan.
Any expericens ??
Thanks in advance
- Murty