On using a metronome....

I see that everyone who is actually any good uses one. Good enough reason for me to start again. I havn't used one in a very long time. My question is, at what point does it make sense NOT to use one? I'm thinking that it could be when you are just figuring out notes on the fretboard, getting your fingers to go where they need be. Or am I dead wrong? Should I be using it right from the beginning even if the tempo is screwed up?

Use a metronome all the time when you need something to keep beat for you. Especially use it when doing scale exercises and things like that. Start off slow and move the tempo up once you have the scale nailed. There is an online metronome here on GT that does it for you automatically. http://www.guitartricks.com/metronome.php

I am rhythmically challanged....there is NOTHING more frustrating that learning a solo or a passage of a song and then finding out that the rhythm is off and you have to re-learn it. This is often more difficult than learning it correctly in the first place.

If you want to be good, always use a metronome. Learn the whole thing together (rhythm and notes). It will make your life and your music much easier. Start slow and work your way up to speed.

If you're just figuring out chords or note combinations then you don't necessarily need to use one all the time. They're good for training you to keep beat with the music as well as increasing your speed.

You might think about getting a drum machine instead of a metronome too.
You can get a much better feel for actually playing to music if you can hear a proper drum beat. Plus you can work on rhythm techniques and different timings.

If you've got the technical knowledge, move into using MIDI files or get something like Band-In-A-Box so you can also practice key changes and different styles of music.

Boss do a good one - the TU-80. Like most Boss/Roland stuff its got way more features packed into it that you'll ever normally need but I've found it essential for all the different timing variations it can produce. Plus its got a tuner built into it as well. Result.

Metronome use is very good and worthwhile...but it depends on what you are practicing. I like to mix up using the metronome for some things and not using it for other stuff.

I think Kev has a point with the drum machine. When I play to a click, I am right on top of it, but that isn't always the feel you're after.

When playing live, if the tune has a laid back groove, I'll be playing very slightly behind the beat - consistently so I'm still 'in time', but a few ms behind it... I think there has to be balance - you want to be in time, but not too robotic...

That said, some sort of click is essential...

Good point Nick. A metronome is a good tool for disciplining yourself but for live work it doesn't have to be that way. Maybe playing with some jam tracks or with other musicians would be better for things like this.

Can't beat playing to a drum machine with a good tight backing track. The problem with a metronome for me is nothing is happening between the clicks, so you can end up with uneven loose rhythms as you rush to meet the click. A backing track with hihats, kick and snare is much easier, throw in some rythmic chopping and you're away. An excellent but very difficult way of nailing solos that require exact timing (eg neoclassical pieces) is to score them out in midi first then play along. The beauty of midi is you can change the bpm to match your skill level then gradually increase it as you get the licks down. If you listen to Rusty Cooley, Theodore Ziras and Yngwie Malmsteen you will notice they play along to a keyboard - with the exception of Yngwie the others are actually playing to a machine. This increases accuracy by a factor of 10 and increasing your abiltiy to get good fast BUT it is very difficult. Also, unless you are consistantly playing straight neo-classical stuff it can sound a little sterile when things get overly accurate an dyou lose the 'swing' feel.

A metronome is designed to program your note count in time. Once your on count it can get old, but can't be beat for picking techniques, especially when string skipping is involved. A drum machine brings life to your playing. I also highly recommend the investment. One song that really helped me on count, whether you like their music or not, is Black Sabbath "Fairies Wear Boots".
The "Time Keeper" (Bill Ward, in case they are too old for some younger players to know) is completely insane in this song. The changes in tempo are an incredible kick-ass count in perfect time. I imagine Ward literally destroying a Little 5 piece studio set while recording this song. I still play it on occasion.