You really have to practice at spy to get the good knowing of how to use him. The soldier and such classes really don't need as much skill....Point and shoot.....However an experienced spy will look ahead of him and decide what he wants to do/take out first. That all in all takes some time...Just my 2cents

P.S. Sorry for the really long post. I probably would've put more into it but I got tired of thinking for now (lol) and just wanted to get some of my views out there.

Valve has already admitted that they will be releasing some crucial updates for the spy to address some of these issues, the most advantageous of which will be that he can refill his cloak meter from the dispenser. Should help a lot.
I don't remember anything official coming from valve about that. Are you sure you aren't confusing it with This?
According to valve:
"Recently, we've received a ton of email asking us if we had accidentally leaked the details of the Spy's unlockables, after Kaanin created this fake web page detailing his version of what the release should contain. His mocked-up image was convincing enough that even some of us at Valve were momentarily fooled. Well played, Kaanin."
Wow, I hadn't seen that before... I can see why people were fooled - pretty official looking.. In fact, I wouldn't really mind if that WAS the update!
only to come back after telling everyone to realise it was community made..Acting is important, but most people are so dang trigger happy anymore that it doesn't matter near as much as it used too.
Oh look it's a teammate that's not doing anything suspicious! *shoot shoot shoot shoot shoot shoot shoot* *spy dies* Oh what do you know it was a spy!
Eliminating, or giving the spy some way to counteract spychecking would go a long way to resolve some of the glaring spy issues.
The spy is just way to easy to discover. Pyro can accidentally set him on fire while he's cloaked or just running by. Spy checking. Can't run through opposing players. Can't run through opposing engi buildings. Can't shoot or loses disguise, I've always thought the spy should be able to shoot at teammates to help keep the disguise going. Like shooting blank ammunition at them so it looks like your actually the class your depicting. Most people notice if your running around them but not shooting at the "enemy". Cloak shimmers if you bump someone while cloaked. Always has main weapon out. Disguises are basically useless except in rare situations.
Still the spy is a fun and challenging class to play, and can be very fun despite the problems.