Other than safety concerns, is there any problem with leaving a G22 loaded ready to fire. In other words, will it weaken the spring or anything like that? I keep it locked in a quick access gun vault and it may sit in there for some time.

A G22 with a round in the chamber is always ready to fire. No problems with springs, etc. although I might consider downloading a high-cap mag by a couple of rounds if it was going to be there for, say, a year or more. I would not do this with a 10rd. mag, however.

Mechanically, there is nothing wrong with leaving a round chambered in your G22.  I'll differ a little from ikor here because I believe it is also OK to leave magazines loaded to full capacity too.  I've always been told that springs lose their tension from repeated use, not sitting in one position for an extended period of time.  I always leave all my magazines loaded to capacity and have never experienced any problems with weakened springs (my Glocks included).

BMANSAR15;

I agree totally, except under, say, conditions where I might load and leave the pistol for a very long time...like my dad did for three years during WWII. Downloading a high-cap by a couple of rounds is just insurance for something like that since it takes a little pressure off of the top round in the mag...which is the one you most have to worry about. Otherwise, yes, load it up to full capacity!

ikor:

I can't argue over the concern over the top round in the magazine.  That's definitely a valid concern.  Somethng to think about.

I always leave my magazines full, NEVER had a problem.  Springs weaken from usage (expansion/compression cycles) much more than sitting expanded or compressed.  My recommendation is leave your magazines full, if you develope any problems (not going to happen), buy replacement springs (cheap) and download your magazines.  I've read about and SEEN numerous cases of magazines that were loaded to capacity and stored for 20+ years and were fired repeatedly without a problem.

From the ammo-oracle.com, but all of it applies to glock factory magazines as well:

What wears out springs are cycles of compression and expansion and also over-compression.  So, every time you "rotate" your mags, you are causing additional wear by cycling the spring.  Loading and unloading magazines will cause more problems than loading and storing them for good.  For best results USGI magazines are probably the best bet because many aftermarket magazines use cheap springs.

One AR15.com member reportedly discovered a fully loaded 20 round USGI mag that was loaded in the Vietnam era.  20 some years later it not only functioned fine but continues to do so.  Others have reported 1911 mags and Luger mags loaded up since World War II that continued to function perfectly when first fired after 40 years.
Q. Shouldn't I be loading my mags with a few less rounds?  If I load them to capacity doesn't that cause reliability problems?
There are three stories about how this got started:

1. If a 20 round magazine was disassembled and reassembled with the spring connected to the follower backwards, it wouldn't feed reliably when fully loaded due to the spring binding in the mag.   Downloading the magazine to 18 became a habit in some circles "just in case," though eventually this problem was discovered, and solders were instructed never to separate the follower from the spring, which virtually eliminated this problem.

2. Many magazines can be loaded without obviously excessive force to 21 rounds, and because ammo was issued loose in boxes during the early Vietnam era, this happened frequently.  The result was often that the first round wouldn't chamber because it was held too tightly in the magazine.  This is not a good thing in a firefight, so early in the history of the M16 it became habit to teach shooters to load 18 in a 20 rounder just to be safe.  Again, the root cause was eventually addressed, and ammo began to be issued on stripper clips, which eliminated the need to count individual rounds when loading mags.

3. Some tactical squads download their back-up magazines by one round to make a tactical reload (which is done with a round chambered and the bolt forward) easier.  This is because of the reduced upward pressure on the rounds.

#3 is probably the only real reason to consider downloading your magazines, though it is generally not necessary.

I not only agree with these guys completely (pretty completely, I keep mine fully loaded) but I've also found a very subtle and positive side affect of this practice.  The obvious one being that when you pick up the gun it will shoot (usually a good thing).  

But the other one is that it automatically makes me think that, every time I even LOOK at one, I'm looking at a LOADED GUN!  

ALL RULES ARE IN EFFECT!

I don't think of myself as being careless with firearms.  That's the problem.  Nobody does.  

It helps me to remember that "a gun is always loaded" isn't just a concept.  In my house, it's probably truth.  So (I hear ya Dad) I tend to watch where it's pointed a little more consciouslyn and, . . . "keep your god damned finger away from that trigger" - I hear ya Dad.  

My G-21 has been loaded for the six years that I have had it.  I carry it everyday.  It gets rained on and is exposed to the elements all the time.  The magazines are kept full at all times and one in the chamber.  I shoot the duty ammo out of it at least every month and replace with fresh ammo.  I have NEVER had a misfeed or misfire.  I would never want a different duty gun.  Just some real-world input for ya.

I've been carrying a Glock 22 since 1995. All mags are fully loaded with a round chambered all the time. As the dept. armorer I'm responsible for 27 Glocks. None has ever had a problem due to the mags being loaded. The idea of downloading your reload mags for a slide forward reload is good, if you think you won't get a positive seat of the mag. But again that has never been a problem for me. I've put about 20000 rds through my Glock without a problem.