Just had my MY2007 with 165,000 miles MOT'ed. Passed but had advisories of rust in various places on the underbody. Inspector was surprised to find that level of rust on a "modern" car, he did not think it would cause a failure for a few more years. There are no issues on the upper body, and the car has seen a below average level of winter salt. 

Anyone else have a rust issue or know if Octavias of this age have a known issue?    

It aint gonna last for ever, is it a 2006 or 56 plate? I'm not a reg snob btw, I keep cars a long time, I traded a 59 plate Saab last year and a 2008 Ford KA my wife drove, but unless you get under the car yourself and treat/paint every stone chip and weld seam then they are going to rust. 14 years is good, and the MOT guy recons it'll last a couple more. If you want it to keep going longer some rust treatment to the underbody won't be that difficult, but probably only going to add an extra couple of years anyway unless really thorough. I'd be tempted to start looking at something newer - you can get too attached to a car and start spending more on keeping than trading.